<?xml version="1.0" encoding="us-ascii"?>
<!--XBRL document created with Toppan Merrill Bridge  10.3.0.9 -->
<!--Based on XBRL 2.1-->
<!--Created on: 8/9/2023 1:38:35 AM-->
<!--Modified on: 8/9/2023 1:38:35 AM-->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#StatementConsolidatedStatementsOfChangesInStockholdersEquity" roleURI="http://www.fsbwa.com/role/StatementConsolidatedStatementsOfChangesInStockholdersEquity" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureServicingRightsTables" roleURI="http://www.fsbwa.com/role/DisclosureServicingRightsTables" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsTables" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsTables" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesDetails" roleURI="http://www.fsbwa.com/role/DisclosureBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureBusinessCombinationDetails" roleURI="http://www.fsbwa.com/role/DisclosureBusinessCombinationDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureBusinessCombinationAmountsRecognizedForAssetsAcquiredAndLiabilitiesAssumedDetails" roleURI="http://www.fsbwa.com/role/DisclosureBusinessCombinationAmountsRecognizedForAssetsAcquiredAndLiabilitiesAssumedDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureInvestmentsSecuritiesReconciliationDetails" roleURI="http://www.fsbwa.com/role/DisclosureInvestmentsSecuritiesReconciliationDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureInvestmentsAllowanceForCreditLossesDetails" roleURI="http://www.fsbwa.com/role/DisclosureInvestmentsAllowanceForCreditLossesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureInvestmentsAmortizedCostOfDebtSecuritiesHeldToMaturityDetails" roleURI="http://www.fsbwa.com/role/DisclosureInvestmentsAmortizedCostOfDebtSecuritiesHeldToMaturityDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureInvestmentsInvestmentSecuritiesDetails" roleURI="http://www.fsbwa.com/role/DisclosureInvestmentsInvestmentSecuritiesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureInvestmentsInvestmentsWithUnrealizedLossesPolicyDetails" roleURI="http://www.fsbwa.com/role/DisclosureInvestmentsInvestmentsWithUnrealizedLossesPolicyDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureInvestmentsAvailableForSaleSecuritiesByContractualMaturityDetails" roleURI="http://www.fsbwa.com/role/DisclosureInvestmentsAvailableForSaleSecuritiesByContractualMaturityDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansCompositionOfLoanPortfolioDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansCompositionOfLoanPortfolioDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAllowanceForCreditLossesOnLoansByLoanCategoriesDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAllowanceForCreditLossesOnLoansByLoanCategoriesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAgingAnalysisOfPastDueLoansDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAgingAnalysisOfPastDueLoansDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansRiskRatedLoanBalancesDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansRiskRatedLoanBalancesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAmortizedCostBasisOfLoansDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAmortizedCostBasisOfLoansDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAmortizedCostBasisOfCollateralDependentImpairedLoansDetails" roleURI="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAmortizedCostBasisOfCollateralDependentImpairedLoansDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureServicingRightsNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureServicingRightsNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureServicingRightsValuationAssumptionsDetails" roleURI="http://www.fsbwa.com/role/DisclosureServicingRightsValuationAssumptionsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureServicingRightsChangesInValuationAssumptionsDetails" roleURI="http://www.fsbwa.com/role/DisclosureServicingRightsChangesInValuationAssumptionsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureDerivativesCumulativeBasisAdjustmentForFairValueHedgesDetails" roleURI="http://www.fsbwa.com/role/DisclosureDerivativesCumulativeBasisAdjustmentForFairValueHedgesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureDerivativesDerivativeInstrumentsDetails" roleURI="http://www.fsbwa.com/role/DisclosureDerivativesDerivativeInstrumentsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureDerivativesEffectOfFairValueAndCashFlowHedgeAccountingDetails" roleURI="http://www.fsbwa.com/role/DisclosureDerivativesEffectOfFairValueAndCashFlowHedgeAccountingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureDerivativesOffsettingDerivativeAssetsDetails" roleURI="http://www.fsbwa.com/role/DisclosureDerivativesOffsettingDerivativeAssetsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureDerivativesCreditRiskRelatedContingentFeaturesDetails" roleURI="http://www.fsbwa.com/role/DisclosureDerivativesCreditRiskRelatedContingentFeaturesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureLeasesDetails" roleURI="http://www.fsbwa.com/role/DisclosureLeasesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureCommitmentsAndContingenciesCommitmentDetails" roleURI="http://www.fsbwa.com/role/DisclosureCommitmentsAndContingenciesCommitmentDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureCommitmentsAndContingenciesNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureCommitmentsAndContingenciesNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsDetails" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsAssetsMeasuredAtFairValueOnNonRecurringBasisDetails" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsAssetsMeasuredAtFairValueOnNonRecurringBasisDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsDiscountRateDetails" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsDiscountRateDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsFairValueLevel3OnRecurringBasisDetails" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsFairValueLevel3OnRecurringBasisDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsFairValueByBalanceSheetGroupingDetails" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsFairValueByBalanceSheetGroupingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureFairValueMeasurementsNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureStockBasedCompensationNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureStockBasedCompensationNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureStockBasedCompensationStockOptionActivityDetails" roleURI="http://www.fsbwa.com/role/DisclosureStockBasedCompensationStockOptionActivityDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureStockBasedCompensationRestrictedStockAwardsDetails" roleURI="http://www.fsbwa.com/role/DisclosureStockBasedCompensationRestrictedStockAwardsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureRegulatoryCapitalNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureRegulatoryCapitalNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureRegulatoryCapitalComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsDetails" roleURI="http://www.fsbwa.com/role/DisclosureRegulatoryCapitalComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureBusinessSegmentsSegmentFinancialResultsDetails" roleURI="http://www.fsbwa.com/role/DisclosureBusinessSegmentsSegmentFinancialResultsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureBusinessSegmentsNarrativeDetails" roleURI="http://www.fsbwa.com/role/DisclosureBusinessSegmentsNarrativeDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureGoodwillAndOtherIntangibleAssetsDetails" roleURI="http://www.fsbwa.com/role/DisclosureGoodwillAndOtherIntangibleAssetsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureRevenueFromContractsWithCustomersDetails" roleURI="http://www.fsbwa.com/role/DisclosureRevenueFromContractsWithCustomersDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <link:roleRef roleURI="http://www.fsbwa.com/role/DisclosureStandardAndCustomAxisDomainDefaults" xlink:type="simple" xlink:href="fsbw-20230630.xsd#DisclosureStandardAndCustomAxisDomainDefaults" />
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-roles-2022.xsd#eedm" />
  <link:arcroleRef arcroleURI="http://www.esma.europa.eu/xbrl/esef/arcrole/wider-narrower" xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/arcrole/esma-arcrole-2018-11-21.xsd#wider-narrower" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" />
  <link:definitionLink xlink:type="extended" xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain" xlink:title="ValuationTechniqueDomain" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_QuotedMarketPricesMember" xlink:label="QuotedMarketPricesMember" xlink:title="QuotedMarketPricesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="QuotedMarketPricesMember" xlink:title="definition: ValuationTechniqueDomain to QuotedMarketPricesMember" use="optional" priority="0" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FairValueOfUnderlyingCollateralMember" xlink:label="FairValueOfUnderlyingCollateralMember" xlink:title="FairValueOfUnderlyingCollateralMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="FairValueOfUnderlyingCollateralMember" xlink:title="definition: ValuationTechniqueDomain to FairValueOfUnderlyingCollateralMember" use="optional" priority="0" order="2" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FairValueOfCollateralMember" xlink:label="FairValueOfCollateralMember" xlink:title="FairValueOfCollateralMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="FairValueOfCollateralMember" xlink:title="definition: ValuationTechniqueDomain to FairValueOfCollateralMember" use="optional" priority="0" order="3" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_IndustrySourcesMember" xlink:label="IndustrySourcesMember" xlink:title="IndustrySourcesMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ValuationTechniqueDomain" xlink:to="IndustrySourcesMember" xlink:title="definition: ValuationTechniqueDomain to IndustrySourcesMember" use="optional" priority="0" order="4" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_PrepaymentSpeedsMember" xlink:label="PrepaymentSpeedsMember" xlink:title="PrepaymentSpeedsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="PrepaymentSpeedsMember" xlink:title="definition: MeasurementInputTypeDomain to PrepaymentSpeedsMember" use="optional" priority="0" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MeasurementInputPullThroughExpectationsMember" xlink:label="MeasurementInputPullThroughExpectationsMember" xlink:title="MeasurementInputPullThroughExpectationsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputPullThroughExpectationsMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputPullThroughExpectationsMember" use="optional" priority="0" order="2" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MeasurementInputDiscountAppliedToObtainedAppraisalMember" xlink:label="MeasurementInputDiscountAppliedToObtainedAppraisalMember" xlink:title="MeasurementInputDiscountAppliedToObtainedAppraisalMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="MeasurementInputTypeDomain" xlink:to="MeasurementInputDiscountAppliedToObtainedAppraisalMember" xlink:title="definition: MeasurementInputTypeDomain to MeasurementInputDiscountAppliedToObtainedAppraisalMember" use="optional" priority="0" order="3" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract" xlink:label="AssetsAbstract" xlink:title="AssetsAbstract" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestReceivable" xlink:label="InterestReceivable" xlink:title="InterestReceivable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AssetsAbstract" xlink:to="InterestReceivable" xlink:title="definition: AssetsAbstract to InterestReceivable" use="optional" priority="0" order="1" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.fsbwa.com/role/DisclosureStandardAndCustomAxisDomainDefaults">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="AdjustmentsForNewAccountingPronouncementsAxis" xlink:title="AdjustmentsForNewAccountingPronouncementsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="TypeOfAdoptionMember" xlink:title="TypeOfAdoptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="TypeOfAdoptionMember" xlink:title="definition: AdjustmentsForNewAccountingPronouncementsAxis to TypeOfAdoptionMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementAxis" xlink:label="RestatementAxis" xlink:title="RestatementAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain" xlink:label="RestatementDomain" xlink:title="RestatementDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RestatementAxis" xlink:to="RestatementDomain" xlink:title="definition: RestatementAxis to RestatementDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:label="ProductOrServiceAxis" xlink:title="ProductOrServiceAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:label="ProductsAndServicesDomain" xlink:title="ProductsAndServicesDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ProductOrServiceAxis" xlink:to="ProductsAndServicesDomain" xlink:title="definition: ProductOrServiceAxis to ProductsAndServicesDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementScenarioAxis" xlink:label="StatementScenarioAxis" xlink:title="StatementScenarioAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="ScenarioUnspecifiedDomain" xlink:title="ScenarioUnspecifiedDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementScenarioAxis" xlink:to="ScenarioUnspecifiedDomain" xlink:title="definition: StatementScenarioAxis to ScenarioUnspecifiedDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:title="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:title="definition: FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis to FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoanRestructuringModificationAxis" xlink:label="LoanRestructuringModificationAxis" xlink:title="LoanRestructuringModificationAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoanRestructuringModificationDomain" xlink:label="LoanRestructuringModificationDomain" xlink:title="LoanRestructuringModificationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LoanRestructuringModificationAxis" xlink:to="LoanRestructuringModificationDomain" xlink:title="definition: LoanRestructuringModificationAxis to LoanRestructuringModificationDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis" xlink:label="LegalEntityAxis" xlink:title="LegalEntityAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain" xlink:label="EntityDomain" xlink:title="EntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LegalEntityAxis" xlink:to="EntityDomain" xlink:title="definition: LegalEntityAxis to EntityDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoanRestructuringModificationNameAxis" xlink:label="LoanRestructuringModificationNameAxis" xlink:title="LoanRestructuringModificationNameAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoanRestructuringModificationNameDomain" xlink:label="LoanRestructuringModificationNameDomain" xlink:title="LoanRestructuringModificationNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LoanRestructuringModificationNameAxis" xlink:to="LoanRestructuringModificationNameDomain" xlink:title="definition: LoanRestructuringModificationNameAxis to LoanRestructuringModificationNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis" xlink:label="LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis" xlink:title="LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesDomain" xlink:label="LoansInsuredOrGuaranteedByGovernmentAuthoritiesDomain" xlink:title="LoansInsuredOrGuaranteedByGovernmentAuthoritiesDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis" xlink:to="LoansInsuredOrGuaranteedByGovernmentAuthoritiesDomain" xlink:title="definition: LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis to LoansInsuredOrGuaranteedByGovernmentAuthoritiesDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="FinancialInstrumentAxis" xlink:title="FinancialInstrumentAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancialInstrumentAxis" xlink:to="TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="definition: FinancialInstrumentAxis to TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="FairValueByMeasurementBasisAxis" xlink:title="FairValueByMeasurementBasisAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="PortionAtFairValueFairValueDisclosureMember" xlink:title="PortionAtFairValueFairValueDisclosureMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementBasisAxis" xlink:to="PortionAtFairValueFairValueDisclosureMember" xlink:title="definition: FairValueByMeasurementBasisAxis to PortionAtFairValueFairValueDisclosureMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="FinancingReceivablePortfolioSegmentAxis" xlink:title="FinancingReceivablePortfolioSegmentAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="FinancingReceivablePortfolioSegmentDomain" xlink:title="FinancingReceivablePortfolioSegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablePortfolioSegmentAxis" xlink:to="FinancingReceivablePortfolioSegmentDomain" xlink:title="definition: FinancingReceivablePortfolioSegmentAxis to FinancingReceivablePortfolioSegmentDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="FairValueByFairValueHierarchyLevelAxis" xlink:title="FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByFairValueHierarchyLevelAxis" xlink:to="FairValueMeasurementsFairValueHierarchyDomain" xlink:title="definition: FairValueByFairValueHierarchyLevelAxis to FairValueMeasurementsFairValueHierarchyDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="FairValueByMeasurementFrequencyAxis" xlink:title="FairValueByMeasurementFrequencyAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="FairValueMeasurementFrequencyDomain" xlink:title="FairValueMeasurementFrequencyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByMeasurementFrequencyAxis" xlink:to="FairValueMeasurementFrequencyDomain" xlink:title="definition: FairValueByMeasurementFrequencyAxis to FairValueMeasurementFrequencyDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:label="InvestmentTypeAxis" xlink:title="InvestmentTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="InvestmentTypeCategorizationMember" xlink:title="InvestmentTypeCategorizationMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="InvestmentTypeAxis" xlink:to="InvestmentTypeCategorizationMember" xlink:title="definition: InvestmentTypeAxis to InvestmentTypeCategorizationMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:label="InformationByCategoryOfDebtSecurityAxis" xlink:title="InformationByCategoryOfDebtSecurityAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:label="OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:title="OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="InformationByCategoryOfDebtSecurityAxis" xlink:to="OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:title="definition: InformationByCategoryOfDebtSecurityAxis to OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="DerivativeInstrumentRiskAxis" xlink:title="DerivativeInstrumentRiskAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="DerivativeContractTypeDomain" xlink:title="DerivativeContractTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DerivativeInstrumentRiskAxis" xlink:to="DerivativeContractTypeDomain" xlink:title="definition: DerivativeInstrumentRiskAxis to DerivativeContractTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FairValueItemPrimaryCategorizationAxisAxis" xlink:label="FairValueItemPrimaryCategorizationAxisAxis" xlink:title="FairValueItemPrimaryCategorizationAxisAxis" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FairValueItemPrimaryCategorizationAxisDomain" xlink:label="FairValueItemPrimaryCategorizationAxisDomain" xlink:title="FairValueItemPrimaryCategorizationAxisDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueItemPrimaryCategorizationAxisAxis" xlink:to="FairValueItemPrimaryCategorizationAxisDomain" xlink:title="definition: FairValueItemPrimaryCategorizationAxisAxis to FairValueItemPrimaryCategorizationAxisDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="ValuationTechniqueAxis" xlink:title="ValuationTechniqueAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="ValuationTechniqueDomain" xlink:title="ValuationTechniqueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ValuationTechniqueAxis" xlink:to="ValuationTechniqueDomain" xlink:title="definition: ValuationTechniqueAxis to ValuationTechniqueDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="MeasurementInputTypeAxis" xlink:title="MeasurementInputTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="MeasurementInputTypeDomain" xlink:title="MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="MeasurementInputTypeAxis" xlink:to="MeasurementInputTypeDomain" xlink:title="definition: MeasurementInputTypeAxis to MeasurementInputTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SignificantUnobservableInputsAxis" xlink:label="SignificantUnobservableInputsAxis" xlink:title="SignificantUnobservableInputsAxis" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SignificantUnobservableInputsDomain" xlink:label="SignificantUnobservableInputsDomain" xlink:title="SignificantUnobservableInputsDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SignificantUnobservableInputsAxis" xlink:to="SignificantUnobservableInputsDomain" xlink:title="definition: SignificantUnobservableInputsAxis to SignificantUnobservableInputsDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="SubsequentEventTypeAxis" xlink:title="SubsequentEventTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="SubsequentEventTypeDomain" xlink:title="SubsequentEventTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsequentEventTypeAxis" xlink:to="SubsequentEventTypeDomain" xlink:title="definition: SubsequentEventTypeAxis to SubsequentEventTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis" xlink:label="StatementGeographicalAxis" xlink:title="StatementGeographicalAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain" xlink:label="SegmentGeographicalDomain" xlink:title="SegmentGeographicalDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementGeographicalAxis" xlink:to="SegmentGeographicalDomain" xlink:title="definition: StatementGeographicalAxis to SegmentGeographicalDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="BalanceSheetLocationAxis" xlink:title="BalanceSheetLocationAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="BalanceSheetLocationDomain" xlink:title="BalanceSheetLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BalanceSheetLocationAxis" xlink:to="BalanceSheetLocationDomain" xlink:title="definition: BalanceSheetLocationAxis to BalanceSheetLocationDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusAxis" xlink:label="PledgedStatusAxis" xlink:title="PledgedStatusAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusDomain" xlink:label="PledgedStatusDomain" xlink:title="PledgedStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PledgedStatusAxis" xlink:to="PledgedStatusDomain" xlink:title="definition: PledgedStatusAxis to PledgedStatusDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis" xlink:label="CumulativeEffectPeriodOfAdoptionAxis" xlink:title="CumulativeEffectPeriodOfAdoptionAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain" xlink:label="CumulativeEffectPeriodOfAdoptionDomain" xlink:title="CumulativeEffectPeriodOfAdoptionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CumulativeEffectPeriodOfAdoptionAxis" xlink:to="CumulativeEffectPeriodOfAdoptionDomain" xlink:title="definition: CumulativeEffectPeriodOfAdoptionAxis to CumulativeEffectPeriodOfAdoptionDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:title="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="HedgingRelationshipDomain" xlink:title="HedgingRelationshipDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="HedgingRelationshipDomain" xlink:title="definition: DerivativeInstrumentsGainLossByHedgingRelationshipAxis to HedgingRelationshipDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis" xlink:label="CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ContractualMaturityAxis" xlink:label="ContractualMaturityAxis" xlink:title="ContractualMaturityAxis" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ContractualMaturity1Domain" xlink:label="ContractualMaturity1Domain" xlink:title="ContractualMaturity1Domain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ContractualMaturityAxis" xlink:to="ContractualMaturity1Domain" xlink:title="definition: ContractualMaturityAxis to ContractualMaturity1Domain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="ConsolidatedEntitiesAxis" xlink:title="ConsolidatedEntitiesAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="ConsolidatedEntitiesDomain" xlink:title="ConsolidatedEntitiesDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConsolidatedEntitiesAxis" xlink:to="ConsolidatedEntitiesDomain" xlink:title="definition: ConsolidatedEntitiesAxis to ConsolidatedEntitiesDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CreditRatingStandardPoorsAxis" xlink:label="CreditRatingStandardPoorsAxis" xlink:title="CreditRatingStandardPoorsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ExternalCreditRatingStandardPoorsMember" xlink:label="ExternalCreditRatingStandardPoorsMember" xlink:title="ExternalCreditRatingStandardPoorsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CreditRatingStandardPoorsAxis" xlink:to="ExternalCreditRatingStandardPoorsMember" xlink:title="definition: CreditRatingStandardPoorsAxis to ExternalCreditRatingStandardPoorsMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:label="InternalCreditAssessmentAxis" xlink:title="InternalCreditAssessmentAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:label="InternalCreditAssessmentDomain" xlink:title="InternalCreditAssessmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="InternalCreditAssessmentAxis" xlink:to="InternalCreditAssessmentDomain" xlink:title="definition: InternalCreditAssessmentAxis to InternalCreditAssessmentDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollateralAxis" xlink:label="CollateralAxis" xlink:title="CollateralAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollateralDomain" xlink:label="CollateralDomain" xlink:title="CollateralDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CollateralAxis" xlink:to="CollateralDomain" xlink:title="definition: CollateralAxis to CollateralDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgingPurposeAxis" xlink:label="PledgingPurposeAxis" xlink:title="PledgingPurposeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgingPurposeDomain" xlink:label="PledgingPurposeDomain" xlink:title="PledgingPurposeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PledgingPurposeAxis" xlink:to="PledgingPurposeDomain" xlink:title="definition: PledgingPurposeAxis to PledgingPurposeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="CashAndCashEquivalentsAxis" xlink:title="CashAndCashEquivalentsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:title="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CashAndCashEquivalentsAxis" xlink:to="RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:title="definition: CashAndCashEquivalentsAxis to RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:label="FinancingReceivablesPeriodPastDueAxis" xlink:title="FinancingReceivablesPeriodPastDueAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="FinancingReceivablesPeriodPastDueDomain" xlink:title="FinancingReceivablesPeriodPastDueDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FinancingReceivablesPeriodPastDueAxis" xlink:to="FinancingReceivablesPeriodPastDueDomain" xlink:title="definition: FinancingReceivablesPeriodPastDueAxis to FinancingReceivablesPeriodPastDueDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationAxis" xlink:label="HedgingDesignationAxis" xlink:title="HedgingDesignationAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain" xlink:label="HedgingDesignationDomain" xlink:title="HedgingDesignationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="HedgingDesignationAxis" xlink:to="HedgingDesignationDomain" xlink:title="definition: HedgingDesignationAxis to HedgingDesignationDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="LossContingenciesByNatureOfContingencyAxis" xlink:title="LossContingenciesByNatureOfContingencyAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="LossContingencyNatureDomain" xlink:title="LossContingencyNatureDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LossContingenciesByNatureOfContingencyAxis" xlink:to="LossContingencyNatureDomain" xlink:title="definition: LossContingenciesByNatureOfContingencyAxis to LossContingencyNatureDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualAxis" xlink:label="TitleOfIndividualAxis" xlink:title="TitleOfIndividualAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="TitleOfIndividualWithRelationshipToEntityDomain" xlink:title="TitleOfIndividualWithRelationshipToEntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TitleOfIndividualAxis" xlink:to="TitleOfIndividualWithRelationshipToEntityDomain" xlink:title="definition: TitleOfIndividualAxis to TitleOfIndividualWithRelationshipToEntityDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="FairValueByAssetClassAxis" xlink:title="FairValueByAssetClassAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:title="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FairValueByAssetClassAxis" xlink:to="FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:title="definition: FairValueByAssetClassAxis to FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingAxis" xlink:label="VestingAxis" xlink:title="VestingAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain" xlink:label="VestingDomain" xlink:title="VestingDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="VestingAxis" xlink:to="VestingDomain" xlink:title="definition: VestingAxis to VestingDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GranteeStatusAxis" xlink:label="GranteeStatusAxis" xlink:title="GranteeStatusAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GranteeStatusDomain" xlink:label="GranteeStatusDomain" xlink:title="GranteeStatusDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="GranteeStatusAxis" xlink:to="GranteeStatusDomain" xlink:title="definition: GranteeStatusAxis to GranteeStatusDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="StatementBusinessSegmentsAxis" xlink:title="StatementBusinessSegmentsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain" xlink:label="SegmentDomain" xlink:title="SegmentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementBusinessSegmentsAxis" xlink:to="SegmentDomain" xlink:title="definition: StatementBusinessSegmentsAxis to SegmentDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis" xlink:label="EquityInterestIssuedOrIssuableByTypeAxis" xlink:title="EquityInterestIssuedOrIssuableByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain" xlink:label="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="EquityInterestIssuedOrIssuableTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="EquityInterestIssuedOrIssuableByTypeAxis" xlink:to="EquityInterestIssuedOrIssuableTypeDomain" xlink:title="definition: EquityInterestIssuedOrIssuableByTypeAxis to EquityInterestIssuedOrIssuableTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CollateralSecurityTypeAxis" xlink:label="CollateralSecurityTypeAxis" xlink:title="CollateralSecurityTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CollateralSecurityTypeDomain" xlink:label="CollateralSecurityTypeDomain" xlink:title="CollateralSecurityTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CollateralSecurityTypeAxis" xlink:to="CollateralSecurityTypeDomain" xlink:title="definition: CollateralSecurityTypeAxis to CollateralSecurityTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="LineOfCreditFacilityAxis" xlink:title="LineOfCreditFacilityAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="LineOfCreditFacilityLenderDomain" xlink:title="LineOfCreditFacilityLenderDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LineOfCreditFacilityAxis" xlink:to="LineOfCreditFacilityLenderDomain" xlink:title="definition: LineOfCreditFacilityAxis to LineOfCreditFacilityLenderDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:label="DebtInstrumentAxis" xlink:title="DebtInstrumentAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="DebtInstrumentNameDomain" xlink:title="DebtInstrumentNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DebtInstrumentAxis" xlink:to="DebtInstrumentNameDomain" xlink:title="definition: DebtInstrumentAxis to DebtInstrumentNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="LongtermDebtTypeAxis" xlink:title="LongtermDebtTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="LongtermDebtTypeDomain" xlink:title="LongtermDebtTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="LongtermDebtTypeAxis" xlink:to="LongtermDebtTypeDomain" xlink:title="definition: LongtermDebtTypeAxis to LongtermDebtTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DefinedContributionPlanContributionMatchCategoryAxis" xlink:label="DefinedContributionPlanContributionMatchCategoryAxis" xlink:title="DefinedContributionPlanContributionMatchCategoryAxis" />
    <link:loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DefinedContributionPlanContributionMatchCategoryDomain" xlink:label="DefinedContributionPlanContributionMatchCategoryDomain" xlink:title="DefinedContributionPlanContributionMatchCategoryDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="DefinedContributionPlanContributionMatchCategoryAxis" xlink:to="DefinedContributionPlanContributionMatchCategoryDomain" xlink:title="definition: DefinedContributionPlanContributionMatchCategoryAxis to DefinedContributionPlanContributionMatchCategoryDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="ConcentrationRiskByTypeAxis" xlink:title="ConcentrationRiskByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="ConcentrationRiskTypeDomain" xlink:title="ConcentrationRiskTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConcentrationRiskByTypeAxis" xlink:to="ConcentrationRiskTypeDomain" xlink:title="definition: ConcentrationRiskByTypeAxis to ConcentrationRiskTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="ConcentrationRiskByBenchmarkAxis" xlink:title="ConcentrationRiskByBenchmarkAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="ConcentrationRiskBenchmarkDomain" xlink:title="ConcentrationRiskBenchmarkDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConcentrationRiskByBenchmarkAxis" xlink:to="ConcentrationRiskBenchmarkDomain" xlink:title="definition: ConcentrationRiskByBenchmarkAxis to ConcentrationRiskBenchmarkDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to AntidilutiveSecuritiesNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareRepurchaseProgramAxis" xlink:label="ShareRepurchaseProgramAxis" xlink:title="ShareRepurchaseProgramAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareRepurchaseProgramDomain" xlink:label="ShareRepurchaseProgramDomain" xlink:title="ShareRepurchaseProgramDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ShareRepurchaseProgramAxis" xlink:to="ShareRepurchaseProgramDomain" xlink:title="definition: ShareRepurchaseProgramAxis to ShareRepurchaseProgramDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1" xlink:title="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" xlink:title="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1 To us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1" order="1" />
  </link:definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/StatementConsolidatedStatementsOfChangesInStockholdersEquity" xlink:type="extended" xlink:title="00400 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountingStandardsUpdate201613Member" xlink:label="us-gaap_AccountingStandardsUpdate201613Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_AccountingStandardsUpdate201613Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockholdersEquity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_SharesOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_NetIncomeLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DividendsCommonStockCash" xlink:label="us-gaap_DividendsCommonStockCash" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_DividendsCommonStockCash" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedDuringPeriodValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockRepurchasedDuringPeriodValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="us-gaap_StockRepurchasedDuringPeriodShares" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockRepurchasedDuringPeriodValue" xlink:to="us-gaap_StockRepurchasedDuringPeriodShares" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" xlink:label="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:to="us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:to="us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTax" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureServicingRightsTables" xlink:type="extended" xlink:title="30503 - Disclosure - SERVICING RIGHTS (Tables)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MortgageServicingRightsMember" xlink:label="fsbw_MortgageServicingRightsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_MortgageServicingRightsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfServicingAssetsAtAmortizedValueTextBlock" xlink:label="us-gaap_ScheduleOfServicingAssetsAtAmortizedValueTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfServicingAssetsAtAmortizedValueTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrServicingLiabilitiesTextBlock" xlink:label="us-gaap_ScheduleOfSensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrServicingLiabilitiesTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfSensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrServicingLiabilitiesTextBlock" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsTables" xlink:type="extended" xlink:title="31103 - Disclosure - FAIR VALUE MEASUREMENTS (Tables)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" xlink:label="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfValuationAllowanceForImpairmentOfRecognizedServicingAssetsTextBlock" xlink:label="us-gaap_ScheduleOfValuationAllowanceForImpairmentOfRecognizedServicingAssetsTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_ScheduleOfValuationAllowanceForImpairmentOfRecognizedServicingAssetsTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock" xlink:label="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByBalanceSheetGroupingTextBlock" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueByBalanceSheetGroupingTextBlock" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="extended" xlink:title="40101 - Disclosure - BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ScheduleOfAccountingPoliciesTable" xlink:label="fsbw_ScheduleOfAccountingPoliciesTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="fsbw_ScheduleOfAccountingPoliciesTable" xlink:to="srt_ProductOrServiceAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RetailDepositMember" xlink:label="fsbw_RetailDepositMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ProductsAndServicesDomain" xlink:to="fsbw_RetailDepositMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="fsbw_ScheduleOfAccountingPoliciesTable" xlink:to="srt_StatementGeographicalAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_PacificNorthwestMember" xlink:label="fsbw_PacificNorthwestMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_SegmentGeographicalDomain" xlink:to="fsbw_PacificNorthwestMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_PugetSoundMember" xlink:label="fsbw_PugetSoundMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_SegmentGeographicalDomain" xlink:to="fsbw_PugetSoundMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ScheduleOfAccountingPoliciesLineItems" xlink:label="fsbw_ScheduleOfAccountingPoliciesLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="fsbw_ScheduleOfAccountingPoliciesLineItems" xlink:to="fsbw_ScheduleOfAccountingPoliciesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfBankBranches" xlink:label="fsbw_NumberOfBankBranches" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="fsbw_ScheduleOfAccountingPoliciesLineItems" xlink:to="fsbw_NumberOfBankBranches" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfAdministrativeOfficesThatAcceptDeposits" xlink:label="fsbw_NumberOfAdministrativeOfficesThatAcceptDeposits" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="fsbw_ScheduleOfAccountingPoliciesLineItems" xlink:to="fsbw_NumberOfAdministrativeOfficesThatAcceptDeposits" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfOperatingSegments" xlink:label="us-gaap_NumberOfOperatingSegments" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="fsbw_ScheduleOfAccountingPoliciesLineItems" xlink:to="us-gaap_NumberOfOperatingSegments" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureBusinessCombinationDetails" xlink:type="extended" xlink:title="40201 - Disclosure - BUSINESS COMBINATION (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ColumbiaStateBankMember" xlink:label="fsbw_ColumbiaStateBankMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fsbw_ColumbiaStateBankMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeDuringPeriodFairValueDisclosureMember" xlink:label="us-gaap_ChangeDuringPeriodFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_ChangeDuringPeriodFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_WorkforceAndCustomerRelationshipsMember" xlink:label="fsbw_WorkforceAndCustomerRelationshipsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="fsbw_WorkforceAndCustomerRelationshipsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationNumberOfBankBranchesAcquired" xlink:label="fsbw_BusinessCombinationNumberOfBankBranchesAcquired" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationNumberOfBankBranchesAcquired" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfBankOwnedBranchesAcquired" xlink:label="fsbw_NumberOfBankOwnedBranchesAcquired" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_NumberOfBankOwnedBranchesAcquired" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Deposits" xlink:label="us-gaap_Deposits" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_Deposits" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationConsiderationTransferredDepositPremiumForCoreDepositsPercent" xlink:label="fsbw_BusinessCombinationConsiderationTransferredDepositPremiumForCoreDepositsPercent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationConsiderationTransferredDepositPremiumForCoreDepositsPercent" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationConsiderationTransferredDepositPremiumForPublicFundsPercent" xlink:label="fsbw_BusinessCombinationConsiderationTransferredDepositPremiumForPublicFundsPercent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationConsiderationTransferredDepositPremiumForPublicFundsPercent" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" xlink:label="us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAcquiredFromAcquisition" xlink:label="us-gaap_CashAcquiredFromAcquisition" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_CashAcquiredFromAcquisition" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationMeasurementPeriod" xlink:label="fsbw_BusinessCombinationMeasurementPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationMeasurementPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationNumberOfLeasesAcquired" xlink:label="fsbw_BusinessCombinationNumberOfLeasesAcquired" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationNumberOfLeasesAcquired" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsLoansAndAssociatedInterestReceivables" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsLoansAndAssociatedInterestReceivables" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsLoansAndAssociatedInterestReceivables" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsFacilitiesAndOtherAssetsNet" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsFacilitiesAndOtherAssetsNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsFacilitiesAndOtherAssetsNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfLoansAcquiredPurchasedFinancialAssetsWithCreditDeterioration" xlink:label="fsbw_NumberOfLoansAcquiredPurchasedFinancialAssetsWithCreditDeterioration" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_NumberOfLoansAcquiredPurchasedFinancialAssetsWithCreditDeterioration" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfLoansExpectedToBeUncollectable" xlink:label="fsbw_NumberOfLoansExpectedToBeUncollectable" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="fsbw_NumberOfLoansExpectedToBeUncollectable" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_Goodwill" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" xlink:label="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureBusinessCombinationAmountsRecognizedForAssetsAcquiredAndLiabilitiesAssumedDetails" xlink:type="extended" xlink:title="40202 - Disclosure - BUSINESS COMBINATION - Amounts Recognized for Assets Acquired and Liabilities Assumed (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_PortionAtOtherThanFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeDuringPeriodFairValueDisclosureMember" xlink:label="us-gaap_ChangeDuringPeriodFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_ChangeDuringPeriodFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ColumbiaStateBankMember" xlink:label="fsbw_ColumbiaStateBankMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fsbw_ColumbiaStateBankMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsInterestReceivables" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsInterestReceivables" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsInterestReceivables" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherRealEstateOwned" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherRealEstateOwned" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherRealEstateOwned" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_Goodwill" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNonInterestBearingDeposits" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNonInterestBearingDeposits" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNonInterestBearingDeposits" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInterestBearingDeposits" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInterestBearingDeposits" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInterestBearingDeposits" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeposits" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterestPayable" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterestPayable" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedInterestPayable" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherLiabilities" xlink:label="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherLiabilities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="fsbw_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherLiabilities" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilitiesAbstract" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureInvestmentsSecuritiesReconciliationDetails" xlink:type="extended" xlink:title="40301 - Disclosure - INVESTMENTS - Securities Reconciliation (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AgencySecuritiesMember" xlink:label="us-gaap_AgencySecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_AgencySecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MunicipalBondsMember" xlink:label="us-gaap_MunicipalBondsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MunicipalBondsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAggregatedInvestmentsMember" xlink:label="us-gaap_OtherAggregatedInvestmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_OtherAggregatedInvestmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesAbstract" xlink:label="us-gaap_AvailableForSaleSecuritiesAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesAbstract" xlink:label="us-gaap_HeldToMaturitySecuritiesAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_HeldToMaturitySecuritiesAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HeldToMaturitySecuritiesAbstract" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_HeldToMaturitySecuritiesAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesFairValue" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_HeldToMaturitySecuritiesAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_HeldToMaturitySecuritiesAbstract" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedGain" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityCumulativeUnrecognizedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAllowanceForCreditLossesExcludingAccruedInterest" xlink:label="fsbw_DebtSecuritiesAllowanceForCreditLossesExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityAbstract" xlink:to="fsbw_DebtSecuritiesAllowanceForCreditLossesExcludingAccruedInterest" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureInvestmentsAllowanceForCreditLossesDetails" xlink:type="extended" xlink:title="40303 - Disclosure - INVESTMENTS - Allowance for Credit Losses (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountingStandardsUpdate201613Member" xlink:label="us-gaap_AccountingStandardsUpdate201613Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="us-gaap_AccountingStandardsUpdate201613Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems" xlink:label="us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureInvestmentsAmortizedCostOfDebtSecuritiesHeldToMaturityDetails" xlink:type="extended" xlink:title="40304 - Disclosure - INVESTMENTS - Amortized Cost of Debt Securities Held-to-Maturity (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CreditRatingStandardPoorsAxis" xlink:label="srt_CreditRatingStandardPoorsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="srt_CreditRatingStandardPoorsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ExternalCreditRatingStandardPoorsMember" xlink:label="srt_ExternalCreditRatingStandardPoorsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CreditRatingStandardPoorsAxis" xlink:to="srt_ExternalCreditRatingStandardPoorsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StandardPoorsBBBRatingMember" xlink:label="srt_StandardPoorsBBBRatingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ExternalCreditRatingStandardPoorsMember" xlink:to="srt_StandardPoorsBBBRatingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StandardPoorsBBPlusRatingMember" xlink:label="srt_StandardPoorsBBPlusRatingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_ExternalCreditRatingStandardPoorsMember" xlink:to="srt_StandardPoorsBBPlusRatingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureInvestmentsInvestmentSecuritiesDetails" xlink:type="extended" xlink:title="40305 - Disclosure - INVESTMENTS - Investment Securities (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralTable" xlink:label="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgingPurposeAxis" xlink:label="us-gaap_PledgingPurposeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralTable" xlink:to="us-gaap_PledgingPurposeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgingPurposeDomain" xlink:label="us-gaap_PledgingPurposeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PledgingPurposeAxis" xlink:to="us-gaap_PledgingPurposeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepositsMember" xlink:label="us-gaap_DepositsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PledgingPurposeDomain" xlink:to="us-gaap_DepositsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_InterestRateSwapCounterpartiesMember" xlink:label="fsbw_InterestRateSwapCounterpartiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PledgingPurposeDomain" xlink:to="fsbw_InterestRateSwapCounterpartiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember" xlink:label="us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_PledgingPurposeDomain" xlink:to="us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems" xlink:label="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems" xlink:to="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancialInstrumentsOwnedCost" xlink:label="fsbw_FinancialInstrumentsOwnedCost" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems" xlink:to="fsbw_FinancialInstrumentsOwnedCost" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancialInstrumentsOwnedAtAmortizedCost" xlink:label="fsbw_FinancialInstrumentsOwnedAtAmortizedCost" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems" xlink:to="fsbw_FinancialInstrumentsOwnedAtAmortizedCost" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentsOwnedAtFairValue" xlink:label="us-gaap_FinancialInstrumentsOwnedAtFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems" xlink:to="us-gaap_FinancialInstrumentsOwnedAtFairValue" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureInvestmentsInvestmentsWithUnrealizedLossesPolicyDetails" xlink:type="extended" xlink:title="40306 - Disclosure - INVESTMENTS - Investments with Unrealized Losses Policy (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AgencySecuritiesMember" xlink:label="us-gaap_AgencySecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_AgencySecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MunicipalBondsMember" xlink:label="us-gaap_MunicipalBondsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MunicipalBondsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAggregatedInvestmentsMember" xlink:label="us-gaap_OtherAggregatedInvestmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_OtherAggregatedInvestmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:label="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsFairValue" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPosition12MonthsOrLongerFairValue" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPosition12MonthsOrLongerFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPosition12MonthsOrLongerFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityUnrealizedLossPositionFairValue" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityUnrealizedLossPositionFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValueAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityUnrealizedLossPositionFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:label="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityUnrealizedLossPositionAccumulatedLoss" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityUnrealizedLossPositionAccumulatedLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLossAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAndHeldToMaturityUnrealizedLossPositionAccumulatedLoss" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureInvestmentsAvailableForSaleSecuritiesByContractualMaturityDetails" xlink:type="extended" xlink:title="40307 - Disclosure - INVESTMENTS - Available for Sale Securities by Contractual Maturity (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DebtSecuritiesAvailableForSaleTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AgencySecuritiesMember" xlink:label="us-gaap_AgencySecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_AgencySecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MunicipalBondsMember" xlink:label="us-gaap_MunicipalBondsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MunicipalBondsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FederalNationalMortgageAssociationFnmaInsuredLoansMember" xlink:label="us-gaap_FederalNationalMortgageAssociationFnmaInsuredLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgageBackedSecuritiesMember" xlink:to="us-gaap_FederalNationalMortgageAssociationFnmaInsuredLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FederalHomeLoanMortgageCorporationFhlmcInsuredLoansMember" xlink:label="us-gaap_FederalHomeLoanMortgageCorporationFhlmcInsuredLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MortgageBackedSecuritiesMember" xlink:to="us-gaap_FederalHomeLoanMortgageCorporationFhlmcInsuredLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GovernmentNationalMortgageAssociationGnmaInsuredLoansMember" xlink:label="us-gaap_GovernmentNationalMortgageAssociationGnmaInsuredLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MortgageBackedSecuritiesMember" xlink:to="us-gaap_GovernmentNationalMortgageAssociationGnmaInsuredLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAggregatedInvestmentsMember" xlink:label="us-gaap_OtherAggregatedInvestmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_OtherAggregatedInvestmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:label="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateYearOne" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateYearOne" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateYearOne" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFive" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFive" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFive" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear10" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear10" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear10" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate" xlink:label="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="fsbw_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="fsbw_DebtSecuritiesAvailableForSaleExcludingAccruedInterestMaturityAllocatedAndSingleMaturityDateAmortizedCostFiscalMaturityAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValue" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesFairValueAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleAndHeldToMaturityFairValue" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansCompositionOfLoanPortfolioDetails" xlink:type="extended" xlink:title="40401 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Composition of Loan Portfolio (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RealEstateLoanPortfolioSegmentMember" xlink:label="fsbw_RealEstateLoanPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fsbw_RealEstateLoanPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgagesMember" xlink:label="us-gaap_MortgagesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_MortgagesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionLoansMember" xlink:label="us-gaap_ConstructionLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_ConstructionLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HomeEquityMember" xlink:label="us-gaap_HomeEquityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_HomeEquityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MultiFamilyRealEstateLoansMember" xlink:label="fsbw_MultiFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_MultiFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerLoanMember" xlink:label="us-gaap_ConsumerLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_ConsumerLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerIndirectHomeImprovementLoansMember" xlink:label="fsbw_ConsumerIndirectHomeImprovementLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerIndirectHomeImprovementLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" xlink:label="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansOtherMember" xlink:label="fsbw_ConsumerLoansOtherMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansOtherMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_WarehouseLendingMember" xlink:label="fsbw_WarehouseLendingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_WarehouseLendingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansNarrativeDetails" xlink:type="extended" xlink:title="40402 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Narrative (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MultiFamilyRealEstateLoansMember" xlink:label="fsbw_MultiFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="fsbw_MultiFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoanRestructuringModificationAxis" xlink:label="us-gaap_LoanRestructuringModificationAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_LoanRestructuringModificationAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoanRestructuringModificationDomain" xlink:label="us-gaap_LoanRestructuringModificationDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_LoanRestructuringModificationAxis" xlink:to="us-gaap_LoanRestructuringModificationDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ExtendedMaturityMember" xlink:label="us-gaap_ExtendedMaturityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LoanRestructuringModificationDomain" xlink:to="us-gaap_ExtendedMaturityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractualInterestRateReductionMember" xlink:label="us-gaap_ContractualInterestRateReductionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LoanRestructuringModificationDomain" xlink:to="us-gaap_ContractualInterestRateReductionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusAxis" xlink:label="us-gaap_PledgedStatusAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_PledgedStatusAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgedStatusDomain" xlink:label="us-gaap_PledgedStatusDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PledgedStatusAxis" xlink:to="us-gaap_PledgedStatusDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetPledgedAsCollateralWithoutRightMember" xlink:label="us-gaap_AssetPledgedAsCollateralWithoutRightMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PledgedStatusDomain" xlink:to="us-gaap_AssetPledgedAsCollateralWithoutRightMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgingPurposeAxis" xlink:label="us-gaap_PledgingPurposeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="6" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_PledgingPurposeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PledgingPurposeDomain" xlink:label="us-gaap_PledgingPurposeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PledgingPurposeAxis" xlink:to="us-gaap_PledgingPurposeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FederalHomeLoanBankAdvancesMember" xlink:label="us-gaap_FederalHomeLoanBankAdvancesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PledgingPurposeDomain" xlink:to="us-gaap_FederalHomeLoanBankAdvancesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="7" xlink:from="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" xlink:to="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_AccountingStandardsUpdate202202Member" xlink:label="fsbw_AccountingStandardsUpdate202202Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TypeOfAdoptionMember" xlink:to="fsbw_AccountingStandardsUpdate202202Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfLoanPortfolioSegments" xlink:label="fsbw_NumberOfLoanPortfolioSegments" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_NumberOfLoanPortfolioSegments" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfWarehouseLendingDivisions" xlink:label="fsbw_NumberOfWarehouseLendingDivisions" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_NumberOfWarehouseLendingDivisions" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalReserveBankLineOfCredit" xlink:label="fsbw_PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalReserveBankLineOfCredit" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalReserveBankLineOfCredit" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_LoansReceivableNumberOfDaysDelinquentToDiscontinueInterestAccrualMinimum" xlink:label="fsbw_LoansReceivableNumberOfDaysDelinquentToDiscontinueInterestAccrualMinimum" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_LoansReceivableNumberOfDaysDelinquentToDiscontinueInterestAccrualMinimum" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:label="us-gaap_FinancingReceivableModificationsNumberOfContracts2" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableModificationsNumberOfContracts2" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableModificationsContractualTerm" xlink:label="fsbw_FinancingReceivableModificationsContractualTerm" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_FinancingReceivableModificationsContractualTerm" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableModificationsContractualInterestRate" xlink:label="fsbw_FinancingReceivableModificationsContractualInterestRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_FinancingReceivableModificationsContractualInterestRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableModificationsRecordedInvestment" xlink:label="us-gaap_FinancingReceivableModificationsRecordedInvestment" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableModificationsRecordedInvestment" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableModificationsPercentage" xlink:label="fsbw_FinancingReceivableModificationsPercentage" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_FinancingReceivableModificationsPercentage" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfUnitsInRealEstateProperty" xlink:label="us-gaap_NumberOfUnitsInRealEstateProperty" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_NumberOfUnitsInRealEstateProperty" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount" xlink:label="us-gaap_FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_FinancingReceivableUnamortizedLoanCommitmentOriginationFeeAndPremiumDiscount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_LoansReceivableDiscountsOnAcquiredLoans" xlink:label="fsbw_LoansReceivableDiscountsOnAcquiredLoans" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="fsbw_LoansReceivableDiscountsOnAcquiredLoans" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNoncurrentAccruedInterestAfterAllowanceForCreditLoss" xlink:label="us-gaap_AccountsReceivableNoncurrentAccruedInterestAfterAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_AccountsReceivableNoncurrentAccruedInterestAfterAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNoncurrentAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList" xlink:label="us-gaap_AccountsReceivableNoncurrentAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_AccountsNotesAndLoansReceivableLineItems" xlink:to="us-gaap_AccountsReceivableNoncurrentAccruedInterestAfterAllowanceForCreditLossStatementOfFinancialPositionExtensibleList" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAllowanceForCreditLossesOnLoansByLoanCategoriesDetails" xlink:type="extended" xlink:title="40403 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Allowance for Credit Losses on Loans by Loan Categories (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RealEstateLoanPortfolioSegmentMember" xlink:label="fsbw_RealEstateLoanPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fsbw_RealEstateLoanPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnallocatedFinancingReceivablesMember" xlink:label="us-gaap_UnallocatedFinancingReceivablesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_UnallocatedFinancingReceivablesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="srt_CumulativeEffectPeriodOfAdoptionAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain" xlink:label="srt_CumulativeEffectPeriodOfAdoptionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CumulativeEffectPeriodOfAdoptionAxis" xlink:to="srt_CumulativeEffectPeriodOfAdoptionDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_CumulativeEffectPeriodOfAdoptionDomain" xlink:to="srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossPeriodIncreaseDecrease" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossPeriodIncreaseDecrease" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRollForward" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossPeriodIncreaseDecrease" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAgingAnalysisOfPastDueLoansDetails" xlink:type="extended" xlink:title="40404 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Aging Analysis of Past Due Loans (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:label="us-gaap_ScheduleOfFinancingReceivablesPastDueTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivables30To59DaysPastDueMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivables60To89DaysPastDueMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NonAccrualFinancingReceivablesMember" xlink:label="fsbw_NonAccrualFinancingReceivablesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="fsbw_NonAccrualFinancingReceivablesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialAssetNotPastDueMember" xlink:label="us-gaap_FinancialAssetNotPastDueMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancialAssetNotPastDueMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialAssetPastDueMember" xlink:label="us-gaap_FinancialAssetPastDueMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="us-gaap_FinancialAssetPastDueMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgagesMember" xlink:label="us-gaap_MortgagesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_MortgagesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RealEstateLoanMember" xlink:label="us-gaap_RealEstateLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_RealEstateLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RealEstateLoanMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionLoansMember" xlink:label="us-gaap_ConstructionLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RealEstateLoanMember" xlink:to="us-gaap_ConstructionLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HomeEquityMember" xlink:label="us-gaap_HomeEquityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_RealEstateLoanMember" xlink:to="us-gaap_HomeEquityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_RealEstateLoanMember" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MultiFamilyRealEstateLoansMember" xlink:label="fsbw_MultiFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_RealEstateLoanMember" xlink:to="fsbw_MultiFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerLoanMember" xlink:label="us-gaap_ConsumerLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_ConsumerLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerIndirectHomeImprovementLoansMember" xlink:label="fsbw_ConsumerIndirectHomeImprovementLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerIndirectHomeImprovementLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" xlink:label="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansOtherMember" xlink:label="fsbw_ConsumerLoansOtherMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansOtherMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_WarehouseLendingMember" xlink:label="fsbw_WarehouseLendingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_WarehouseLendingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RealEstateLoanPortfolioSegmentMember" xlink:label="fsbw_RealEstateLoanPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fsbw_RealEstateLoanPortfolioSegmentMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivablesPastDueTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfLoansAccruingInterest" xlink:label="fsbw_NumberOfLoansAccruingInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="fsbw_NumberOfLoansAccruingInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfTroubledDebtRestructuredLoans" xlink:label="fsbw_NumberOfTroubledDebtRestructuredLoans" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="fsbw_NumberOfTroubledDebtRestructuredLoans" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfTdrsIncurringDefaultWithinTwelveMonthsOfRestructure" xlink:label="fsbw_NumberOfTdrsIncurringDefaultWithinTwelveMonthsOfRestructure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="fsbw_NumberOfTdrsIncurringDefaultWithinTwelveMonthsOfRestructure" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansRiskRatedLoanBalancesDetails" xlink:type="extended" xlink:title="40405 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Risk Rated Loan Balances (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RealEstateLoanPortfolioSegmentMember" xlink:label="fsbw_RealEstateLoanPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fsbw_RealEstateLoanPortfolioSegmentMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InternalCreditAssessmentAxis" xlink:label="us-gaap_InternalCreditAssessmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_InternalCreditAssessmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InternalCreditAssessmentDomain" xlink:label="us-gaap_InternalCreditAssessmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InternalCreditAssessmentAxis" xlink:to="us-gaap_InternalCreditAssessmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PassMember" xlink:label="us-gaap_PassMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_PassMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_WatchMember" xlink:label="fsbw_WatchMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="fsbw_WatchMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SpecialMentionMember" xlink:label="us-gaap_SpecialMentionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_SpecialMentionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubstandardMember" xlink:label="us-gaap_SubstandardMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_InternalCreditAssessmentDomain" xlink:to="us-gaap_SubstandardMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgagesMember" xlink:label="us-gaap_MortgagesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_MortgagesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionLoansMember" xlink:label="us-gaap_ConstructionLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_ConstructionLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HomeEquityMember" xlink:label="us-gaap_HomeEquityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_HomeEquityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MultiFamilyRealEstateLoansMember" xlink:label="fsbw_MultiFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_MultiFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerLoanMember" xlink:label="us-gaap_ConsumerLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_ConsumerLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerIndirectHomeImprovementLoansMember" xlink:label="fsbw_ConsumerIndirectHomeImprovementLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerIndirectHomeImprovementLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" xlink:label="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansOtherMember" xlink:label="fsbw_ConsumerLoansOtherMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansOtherMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_WarehouseLendingMember" xlink:label="fsbw_WarehouseLendingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_WarehouseLendingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolving" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestRevolving" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestRevolving" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff" xlink:label="fsbw_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff" xlink:label="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAmortizedCostBasisOfLoansDetails" xlink:type="extended" xlink:title="40406 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Amortized Cost Basis of Loans (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RealEstateLoanPortfolioSegmentMember" xlink:label="fsbw_RealEstateLoanPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fsbw_RealEstateLoanPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgagesMember" xlink:label="us-gaap_MortgagesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_MortgagesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HomeEquityMember" xlink:label="us-gaap_HomeEquityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_HomeEquityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerLoanMember" xlink:label="us-gaap_ConsumerLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_ConsumerLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerIndirectHomeImprovementLoansMember" xlink:label="fsbw_ConsumerIndirectHomeImprovementLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerIndirectHomeImprovementLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" xlink:label="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansOtherMember" xlink:label="fsbw_ConsumerLoansOtherMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansOtherMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableNonaccrualNoAllowance" xlink:label="us-gaap_FinancingReceivableNonaccrualNoAllowance" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableNonaccrualNoAllowance" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FinancingReceivableNonAccrualWithAllowanceForCreditLosses" xlink:label="fsbw_FinancingReceivableNonAccrualWithAllowanceForCreditLosses" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_FinancingReceivableNonAccrualWithAllowanceForCreditLosses" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableNonaccrualInterestIncome" xlink:label="us-gaap_FinancingReceivableNonaccrualInterestIncome" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_FinancingReceivableNonaccrualInterestIncome" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLoansReceivableAndAllowanceForCreditLossesLoansAmortizedCostBasisOfCollateralDependentImpairedLoansDetails" xlink:type="extended" xlink:title="40407 - Disclosure - LOANS RECEIVABLE AND ALLOWANCE FOR CREDIT LOSSES - LOANS - Amortized Cost Basis of Collateral Dependent Impaired Loans (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentAxis" xlink:to="us-gaap_FinancingReceivablePortfolioSegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RealEstateLoanPortfolioSegmentMember" xlink:label="fsbw_RealEstateLoanPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="fsbw_RealEstateLoanPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerPortfolioSegmentMember" xlink:label="us-gaap_ConsumerPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_ConsumerPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialPortfolioSegmentMember" xlink:label="us-gaap_CommercialPortfolioSegmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivablePortfolioSegmentDomain" xlink:to="us-gaap_CommercialPortfolioSegmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollateralAxis" xlink:label="us-gaap_CollateralAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_CollateralAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollateralDomain" xlink:label="us-gaap_CollateralDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RealEstateMember" xlink:label="us-gaap_RealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_RealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RealEstateMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResidentialRealEstateMember" xlink:label="us-gaap_ResidentialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_RealEstateMember" xlink:to="us-gaap_ResidentialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquipmentMember" xlink:label="us-gaap_EquipmentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_EquipmentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgagesMember" xlink:label="us-gaap_MortgagesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_MortgagesMember" use="optional" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HomeEquityMember" xlink:label="us-gaap_HomeEquityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_HomeEquityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerLoanMember" xlink:label="us-gaap_ConsumerLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_ConsumerLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerIndirectHomeImprovementLoansMember" xlink:label="fsbw_ConsumerIndirectHomeImprovementLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerIndirectHomeImprovementLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" xlink:label="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ConsumerLoanMember" xlink:to="fsbw_ConsumerLoansMarineLoanFinancingReceivableMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ImpairedLoansCollateral" xlink:label="fsbw_ImpairedLoansCollateral" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="fsbw_ImpairedLoansCollateral" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureServicingRightsNarrativeDetails" xlink:type="extended" xlink:title="40501 - Disclosure - SERVICING RIGHTS - Narrative (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MortgageServicingRightsMember" xlink:label="fsbw_MortgageServicingRightsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_MortgageServicingRightsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" xlink:label="us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountAsset" xlink:label="us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountAsset" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountAsset" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets" xlink:label="us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureServicingRightsValuationAssumptionsDetails" xlink:type="extended" xlink:title="40503 - Disclosure - SERVICING RIGHTS - Valuation Assumptions (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MortgageServicingRightsMember" xlink:label="fsbw_MortgageServicingRightsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_MortgageServicingRightsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate" xlink:label="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed" xlink:label="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1" xlink:label="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageLife1" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureServicingRightsChangesInValuationAssumptionsDetails" xlink:type="extended" xlink:title="40504 - Disclosure - SERVICING RIGHTS - Changes in Valuation Assumptions (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MortgageServicingRightsMember" xlink:label="fsbw_MortgageServicingRightsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_MortgageServicingRightsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestsContinuedToBeHeldByTransferorFairValue" xlink:label="us-gaap_InterestsContinuedToBeHeldByTransferorFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_InterestsContinuedToBeHeldByTransferorFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageRateOfNote" xlink:label="fsbw_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageRateOfNote" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueWeightedAverageRateOfNote" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueBasisPointsDropInNoteRateAssumptionOne" xlink:label="fsbw_ServicingLiabilityAtFairValueBasisPointsDropInNoteRateAssumptionOne" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueBasisPointsDropInNoteRateAssumptionOne" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueBasisPointsDropInNoteRateAssumptionTwo" xlink:label="fsbw_ServicingLiabilityAtFairValueBasisPointsDropInNoteRateAssumptionTwo" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueBasisPointsDropInNoteRateAssumptionTwo" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed" xlink:label="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsConditionalRepaymentRateAfter0.5AdverseChangeInNoteRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsConditionalRepaymentRateAfter0.5AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsConditionalRepaymentRateAfter0.5AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsConditionalRepaymentRateAfter1AdverseChangeInNoteRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsConditionalRepaymentRateAfter1AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsConditionalRepaymentRateAfter1AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetAtFairValueAmount" xlink:label="us-gaap_ServicingAssetAtFairValueAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ServicingAssetAtFairValueAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter0.5AdverseChangeInNoteRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter0.5AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter0.5AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter1AdverseChangeInNoteRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter1AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter1AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalance" xlink:label="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalance" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalance" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter0.5AdverseChangeInNoteRate" xlink:label="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter0.5AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter0.5AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter1AdverseChangeInNoteRate" xlink:label="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter1AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter1AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate" xlink:label="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsDiscountRateAfter0.5AdverseChangeInNoteRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsDiscountRateAfter0.5AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsDiscountRateAfter0.5AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsDiscountRateAfter1AdverseChangeInNoteRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsDiscountRateAfter1AdverseChangeInNoteRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsDiscountRateAfter1AdverseChangeInNoteRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter0.5AdverseChangeInDiscountRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter0.5AdverseChangeInDiscountRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter0.5AdverseChangeInDiscountRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter1AdverseChangeInDiscountRate" xlink:label="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter1AdverseChangeInDiscountRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_SensitivityAnalysisOfFairValueTransferorsInterestsInTransferredFinancialAssetsAmountAfter1AdverseChangeInDiscountRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter0.5AdverseChangeInDiscountRate" xlink:label="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter0.5AdverseChangeInDiscountRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter0.5AdverseChangeInDiscountRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter1AdverseChangeInDiscountRate" xlink:label="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter1AdverseChangeInDiscountRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="fsbw_ServicingLiabilityAtFairValueSingleFamilyMortgageServicingRightsAsAPercentageOfAggregatePortfolioPrincipalBalanceAfter1AdverseChangeInDiscountRate" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureDerivativesCumulativeBasisAdjustmentForFairValueHedgesDetails" xlink:type="extended" xlink:title="40602 - Disclosure - DERIVATIVES - Cumulative-basis Adjustment for Fair Value Hedges (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="us-gaap_HedgingRelationshipDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="us-gaap_HedgingRelationshipDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueHedgingMember" xlink:label="us-gaap_FairValueHedgingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingRelationshipDomain" xlink:to="us-gaap_FairValueHedgingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:label="us-gaap_DerivativeInstrumentsGainLossLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_HedgedAssetsLiabilitiesCarryingAmount" xlink:label="fsbw_HedgedAssetsLiabilitiesCarryingAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="fsbw_HedgedAssetsLiabilitiesCarryingAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CumulativeAmountOfFairValueHedgingAdjustmentIncludedInCarryingAmountOfHedgedAssetsLiabilities" xlink:label="fsbw_CumulativeAmountOfFairValueHedgingAdjustmentIncludedInCarryingAmountOfHedgedAssetsLiabilities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="fsbw_CumulativeAmountOfFairValueHedgingAdjustmentIncludedInCarryingAmountOfHedgedAssetsLiabilities" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DerivativeHedgingAmortizedCostBasisOfClosedPortfolios" xlink:label="fsbw_DerivativeHedgingAmortizedCostBasisOfClosedPortfolios" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="fsbw_DerivativeHedgingAmortizedCostBasisOfClosedPortfolios" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeAmountOfHedgedItem" xlink:label="us-gaap_DerivativeAmountOfHedgedItem" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeAmountOfHedgedItem" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureDerivativesDerivativeInstrumentsDetails" xlink:type="extended" xlink:title="40603 - Disclosure - DERIVATIVES - Derivative instruments (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeTable" xlink:label="us-gaap_DerivativeTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationAxis" xlink:label="us-gaap_HedgingDesignationAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_HedgingDesignationAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain" xlink:label="us-gaap_HedgingDesignationDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_HedgingDesignationAxis" xlink:to="us-gaap_HedgingDesignationDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DesignatedAsHedgingInstrumentMember" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_DesignatedAsHedgingInstrumentMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NondesignatedMember" xlink:label="us-gaap_NondesignatedMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_HedgingDesignationDomain" xlink:to="us-gaap_NondesignatedMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateLockCommitmentsMember" xlink:label="us-gaap_InterestRateLockCommitmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateLockCommitmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MandatoryAndBestEffortForwardCommitmentsMember" xlink:label="fsbw_MandatoryAndBestEffortForwardCommitmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="fsbw_MandatoryAndBestEffortForwardCommitmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgageBackedSecuritiesOtherMember" xlink:label="us-gaap_MortgageBackedSecuritiesOtherMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_MortgageBackedSecuritiesOtherMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CustomerSwapPositionsMember" xlink:label="fsbw_CustomerSwapPositionsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="fsbw_CustomerSwapPositionsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DealerOffsetsToCustomerSwapPositionsMember" xlink:label="fsbw_DealerOffsetsToCustomerSwapPositionsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="fsbw_DealerOffsetsToCustomerSwapPositionsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_DerivativeTable" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="us-gaap_HedgingRelationshipDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="us-gaap_HedgingRelationshipDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashFlowHedgingMember" xlink:label="us-gaap_CashFlowHedgingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingRelationshipDomain" xlink:to="us-gaap_CashFlowHedgingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueHedgingMember" xlink:label="us-gaap_FairValueHedgingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_HedgingRelationshipDomain" xlink:to="us-gaap_FairValueHedgingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeLineItems" xlink:label="us-gaap_DerivativeLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeNotionalAmount" xlink:label="us-gaap_DerivativeNotionalAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_DerivativeNotionalAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateDerivativeAssetsAtFairValue" xlink:label="us-gaap_InterestRateDerivativeAssetsAtFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_InterestRateDerivativeAssetsAtFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateDerivativeLiabilitiesAtFairValue" xlink:label="us-gaap_InterestRateDerivativeLiabilitiesAtFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeLineItems" xlink:to="us-gaap_InterestRateDerivativeLiabilitiesAtFairValue" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureDerivativesEffectOfFairValueAndCashFlowHedgeAccountingDetails" xlink:type="extended" xlink:title="40604 - Disclosure - DERIVATIVES - Effect of Fair Value and Cash Flow Hedge Accounting (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingRelationshipDomain" xlink:label="us-gaap_HedgingRelationshipDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis" xlink:to="us-gaap_HedgingRelationshipDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueHedgingMember" xlink:label="us-gaap_FairValueHedgingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_HedgingRelationshipDomain" xlink:to="us-gaap_FairValueHedgingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashFlowHedgingMember" xlink:label="us-gaap_CashFlowHedgingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_HedgingRelationshipDomain" xlink:to="us-gaap_CashFlowHedgingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" xlink:to="us-gaap_IncomeStatementLocationAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseMember" xlink:label="us-gaap_InterestExpenseMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_InterestExpenseMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestIncomeMember" xlink:label="us-gaap_InterestIncomeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_InterestIncomeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:label="us-gaap_DerivativeInstrumentsGainLossLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeGainLossOnDerivativeNet" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeGainLossOnDerivativeNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1" xlink:label="us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_ChangeInUnrealizedGainLossOnHedgedItemInFairValueHedge1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1" xlink:label="us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss" xlink:label="us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_DerivativeFairValueHedgeIncludedInEffectivenessGainLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossFromComponentsExcludedFromAssessmentOfCashFlowHedgeEffectivenessNet" xlink:label="us-gaap_GainLossFromComponentsExcludedFromAssessmentOfCashFlowHedgeEffectivenessNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="us-gaap_GainLossFromComponentsExcludedFromAssessmentOfCashFlowHedgeEffectivenessNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_GainLossOnChangeInFairValueOfNonhedgingDerivatives" xlink:label="fsbw_GainLossOnChangeInFairValueOfNonhedgingDerivatives" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_DerivativeInstrumentsGainLossLineItems" xlink:to="fsbw_GainLossOnChangeInFairValueOfNonhedgingDerivatives" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureDerivativesOffsettingDerivativeAssetsDetails" xlink:type="extended" xlink:title="40605 - Disclosure - DERIVATIVES - Offsetting Derivative Assets (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OffsettingAssetsTable" xlink:label="us-gaap_OffsettingAssetsTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_OffsettingAssetsTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OffsettingAssetsLineItems" xlink:label="us-gaap_OffsettingAssetsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_OffsettingAssetsLineItems" xlink:to="us-gaap_OffsettingAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OffsettingAssetsLineItems" xlink:to="us-gaap_DerivativeFairValueOfDerivativeAsset" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeAssets" xlink:label="us-gaap_DerivativeAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_OffsettingAssetsLineItems" xlink:to="us-gaap_DerivativeAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeAssetFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" xlink:label="us-gaap_DerivativeAssetFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_OffsettingAssetsLineItems" xlink:to="us-gaap_DerivativeAssetFairValueOffsetAgainstCollateralNetOfNotSubjectToMasterNettingArrangementPolicyElection" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureDerivativesCreditRiskRelatedContingentFeaturesDetails" xlink:type="extended" xlink:title="40607 - Disclosure - DERIVATIVES - Credit-risk-related Contingent Features (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:label="us-gaap_ScheduleOfImpairedFinancingReceivableTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollateralAxis" xlink:label="us-gaap_CollateralAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfImpairedFinancingReceivableTable" xlink:to="us-gaap_CollateralAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CollateralDomain" xlink:label="us-gaap_CollateralDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_CollateralAxis" xlink:to="us-gaap_CollateralDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CollateralDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CollateralForTbaTradesMember" xlink:label="fsbw_CollateralForTbaTradesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CollateralDomain" xlink:to="fsbw_CollateralForTbaTradesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableImpairedLineItems" xlink:label="us-gaap_FinancingReceivableImpairedLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_ScheduleOfImpairedFinancingReceivableTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeCreditRiskRelatedContingentFeaturesAbstract" xlink:label="us-gaap_DerivativeCreditRiskRelatedContingentFeaturesAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableImpairedLineItems" xlink:to="us-gaap_DerivativeCreditRiskRelatedContingentFeaturesAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeNetLiabilityPositionAggregateFairValue" xlink:label="us-gaap_DerivativeNetLiabilityPositionAggregateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeCreditRiskRelatedContingentFeaturesAbstract" xlink:to="us-gaap_DerivativeNetLiabilityPositionAggregateFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CollateralAlreadyPostedCarryingValue" xlink:label="fsbw_CollateralAlreadyPostedCarryingValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeCreditRiskRelatedContingentFeaturesAbstract" xlink:to="fsbw_CollateralAlreadyPostedCarryingValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCollateralForBorrowedSecurities" xlink:label="us-gaap_CashCollateralForBorrowedSecurities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_DerivativeCreditRiskRelatedContingentFeaturesAbstract" xlink:to="us-gaap_CashCollateralForBorrowedSecurities" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureLeasesDetails" xlink:type="extended" xlink:title="40701 - Disclosure - LEASES (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionTable" xlink:label="us-gaap_LesseeLeaseDescriptionTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_LesseeLeaseDescriptionTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionLineItems" xlink:label="us-gaap_LesseeLeaseDescriptionLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_LesseeLeaseDescriptionLineItems" xlink:to="us-gaap_LesseeLeaseDescriptionTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseTermOfContract" xlink:label="us-gaap_LesseeOperatingLeaseTermOfContract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LesseeLeaseDescriptionLineItems" xlink:to="us-gaap_LesseeOperatingLeaseTermOfContract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" xlink:label="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LesseeLeaseDescriptionLineItems" xlink:to="us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm" xlink:label="us-gaap_LesseeOperatingLeaseRenewalTerm" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LesseeLeaseDescriptionLineItems" xlink:to="us-gaap_LesseeOperatingLeaseRenewalTerm" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureCommitmentsAndContingenciesCommitmentDetails" xlink:type="extended" xlink:title="41001 - Disclosure - COMMITMENTS AND CONTINGENCIES - Commitment (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsToExtendCreditMember" xlink:label="us-gaap_CommitmentsToExtendCreditMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CommitmentsToExtendCreditMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgagesMember" xlink:label="us-gaap_MortgagesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_MortgagesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialRealEstateMember" xlink:label="us-gaap_CommercialRealEstateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_CommercialRealEstateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionLoansMember" xlink:label="us-gaap_ConstructionLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_ConstructionLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HomeEquityMember" xlink:label="us-gaap_HomeEquityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MortgagesMember" xlink:to="us-gaap_HomeEquityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MultiFamilyRealEstateLoansMember" xlink:label="fsbw_MultiFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MortgagesMember" xlink:to="fsbw_MultiFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsumerLoanMember" xlink:label="us-gaap_ConsumerLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_ConsumerLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommercialLoanMember" xlink:label="us-gaap_CommercialLoanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="us-gaap_CommercialLoanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndIndustrialMember" xlink:label="fsbw_CommercialAndIndustrialMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_CommercialAndIndustrialMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_WarehouseLendingMember" xlink:label="fsbw_WarehouseLendingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CommercialLoanMember" xlink:to="fsbw_WarehouseLendingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" xlink:label="us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems" xlink:to="us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureCommitmentsAndContingenciesNarrativeDetails" xlink:type="extended" xlink:title="41002 - Disclosure - COMMITMENTS AND CONTINGENCIES - Narrative (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable" xlink:label="us-gaap_LossContingenciesTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_LossContingenciesTable" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OneToFourFamilyRealEstateLoansMember" xlink:label="fsbw_OneToFourFamilyRealEstateLoansMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="fsbw_OneToFourFamilyRealEstateLoansMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_LossContingenciesTable" xlink:to="us-gaap_LossContingenciesByNatureOfContingencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="us-gaap_LossContingencyNatureDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:to="us-gaap_LossContingencyNatureDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GuaranteeOfIndebtednessOfOthersMember" xlink:label="us-gaap_GuaranteeOfIndebtednessOfOthersMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_LossContingencyNatureDomain" xlink:to="us-gaap_GuaranteeOfIndebtednessOfOthersMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_LossContingenciesTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_LossContingenciesTable" xlink:to="srt_TitleOfIndividualAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ChiefExecutiveOfficerMember" xlink:label="srt_ChiefExecutiveOfficerMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="srt_ChiefExecutiveOfficerMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems" xlink:label="us-gaap_LossContingenciesLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_LossContingenciesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_AllowanceForCreditLossesOnUnfundedLoanCommitments" xlink:label="fsbw_AllowanceForCreditLossesOnUnfundedLoanCommitments" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_AllowanceForCreditLossesOnUnfundedLoanCommitments" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SaleOfLoansToFederalHomeLoanBank" xlink:label="fsbw_SaleOfLoansToFederalHomeLoanBank" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_SaleOfLoansToFederalHomeLoanBank" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FederalHomeLoanBankFirstLossAccountEstablished" xlink:label="fsbw_FederalHomeLoanBankFirstLossAccountEstablished" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_FederalHomeLoanBankFirstLossAccountEstablished" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FederalHomeLoanBankRecourseObligation" xlink:label="fsbw_FederalHomeLoanBankRecourseObligation" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_FederalHomeLoanBankRecourseObligation" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FederalHomeLoanBankRecourseObligationPercentageOfLoansOutstanding" xlink:label="fsbw_FederalHomeLoanBankRecourseObligationPercentageOfLoansOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_FederalHomeLoanBankRecourseObligationPercentageOfLoansOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_AllowanceForLoanAndLeaseLossesLoansSoldPercentageOfOutstandingCreditEnhancement" xlink:label="fsbw_AllowanceForLoanAndLeaseLossesLoansSoldPercentageOfOutstandingCreditEnhancement" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_AllowanceForLoanAndLeaseLossesLoansSoldPercentageOfOutstandingCreditEnhancement" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllowanceForLoanAndLeaseLossesLoansSold" xlink:label="us-gaap_AllowanceForLoanAndLeaseLossesLoansSold" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_AllowanceForLoanAndLeaseLossesLoansSold" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OutstandingDelinquenciesOnLoansSoldToFederalHomeLoanBank" xlink:label="fsbw_OutstandingDelinquenciesOnLoansSoldToFederalHomeLoanBank" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_OutstandingDelinquenciesOnLoansSoldToFederalHomeLoanBank" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyAccrualAtCarryingValue" xlink:label="us-gaap_LossContingencyAccrualAtCarryingValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_LossContingencyAccrualAtCarryingValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_SeveranceAgreementPeriodOfBaseCompensationDisbursedAsLumpSumPayment" xlink:label="fsbw_SeveranceAgreementPeriodOfBaseCompensationDisbursedAsLumpSumPayment" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_SeveranceAgreementPeriodOfBaseCompensationDisbursedAsLumpSumPayment" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ChangeOfControlAgreementNoticeRequiredToCancelAgreementPeriod" xlink:label="fsbw_ChangeOfControlAgreementNoticeRequiredToCancelAgreementPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_ChangeOfControlAgreementNoticeRequiredToCancelAgreementPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ChangeOfControlAgreementExecutivePaymentPeriodPriorToChangeInControl" xlink:label="fsbw_ChangeOfControlAgreementExecutivePaymentPeriodPriorToChangeInControl" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_ChangeOfControlAgreementExecutivePaymentPeriodPriorToChangeInControl" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ChangeOfControlAgreementExecutivePaymentPeriodFollowingChangeInControl" xlink:label="fsbw_ChangeOfControlAgreementExecutivePaymentPeriodFollowingChangeInControl" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_ChangeOfControlAgreementExecutivePaymentPeriodFollowingChangeInControl" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ChangeOfControlAgreementPeriodOfBaseCompensationDisbursedAsLumpSumPayment" xlink:label="fsbw_ChangeOfControlAgreementPeriodOfBaseCompensationDisbursedAsLumpSumPayment" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_ChangeOfControlAgreementPeriodOfBaseCompensationDisbursedAsLumpSumPayment" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyPendingClaimsNumber" xlink:label="us-gaap_LossContingencyPendingClaimsNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_LossContingencyPendingClaimsNumber" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_AllowanceForCreditLossesOnUnfundedLoanCommitmentsProvisionRecovery" xlink:label="fsbw_AllowanceForCreditLossesOnUnfundedLoanCommitmentsProvisionRecovery" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="fsbw_AllowanceForCreditLossesOnUnfundedLoanCommitmentsProvisionRecovery" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsDetails" xlink:type="extended" xlink:title="41101 - Disclosure - FAIR VALUE MEASUREMENTS (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_InformationByCategoryOfDebtSecurityAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_InformationByCategoryOfDebtSecurityAxis" xlink:to="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableforsaleSecuritiesMember" xlink:label="us-gaap_AvailableforsaleSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:to="us-gaap_AvailableforsaleSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeMember" xlink:label="us-gaap_DerivativeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain" xlink:to="us-gaap_DerivativeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AgencySecuritiesMember" xlink:label="us-gaap_AgencySecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_AgencySecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MunicipalBondsMember" xlink:label="us-gaap_MunicipalBondsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MunicipalBondsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="us-gaap_MortgageBackedSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_MortgageBackedSecuritiesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAggregatedInvestmentsMember" xlink:label="us-gaap_OtherAggregatedInvestmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_OtherAggregatedInvestmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MortgageLoansHeldForSaleMember" xlink:label="fsbw_MortgageLoansHeldForSaleMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_MortgageLoansHeldForSaleMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateLockCommitmentsMember" xlink:label="us-gaap_InterestRateLockCommitmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_InterestRateLockCommitmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember" xlink:label="us-gaap_InterestRateSwapMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_InterestRateSwapMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MandatoryAndBestEffortForwardCommitmentsWithInvestorsMember" xlink:label="fsbw_MandatoryAndBestEffortForwardCommitmentsWithInvestorsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_MandatoryAndBestEffortForwardCommitmentsWithInvestorsMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ForwardTbaMortgageBackedSecuritiesMember" xlink:label="fsbw_ForwardTbaMortgageBackedSecuritiesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="fsbw_ForwardTbaMortgageBackedSecuritiesMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResidentialMortgageMember" xlink:label="us-gaap_ResidentialMortgageMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ResidentialMortgageMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="us-gaap_AssetsFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_AssetsFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableFairValueDisclosure" xlink:label="us-gaap_LoansReceivableFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_LoansReceivableFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialLiabilitiesFairValueDisclosure" xlink:label="us-gaap_FinancialLiabilitiesFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FinancialLiabilitiesFairValueDisclosure" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsAssetsMeasuredAtFairValueOnNonRecurringBasisDetails" xlink:type="extended" xlink:title="41102 - Disclosure - FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on a Non-recurring Basis (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingRights" xlink:label="fsbw_ServicingRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="fsbw_ServicingRights" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsDiscountRateDetails" xlink:type="extended" xlink:title="41103 - Disclosure - FAIR VALUE MEASUREMENTS - Discount Rate (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateLockCommitmentsMember" xlink:label="us-gaap_InterestRateLockCommitmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateLockCommitmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForwardContractsMember" xlink:label="us-gaap_ForwardContractsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForwardContractsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FairValueItemPrimaryCategorizationAxisAxis" xlink:label="fsbw_FairValueItemPrimaryCategorizationAxisAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="fsbw_FairValueItemPrimaryCategorizationAxisAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FairValueItemPrimaryCategorizationAxisDomain" xlink:label="fsbw_FairValueItemPrimaryCategorizationAxisDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="fsbw_FairValueItemPrimaryCategorizationAxisAxis" xlink:to="fsbw_FairValueItemPrimaryCategorizationAxisDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ServicingRightsMember" xlink:label="fsbw_ServicingRightsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="fsbw_FairValueItemPrimaryCategorizationAxisDomain" xlink:to="fsbw_ServicingRightsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_WeightedAverageMember" xlink:label="srt_WeightedAverageMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_RangeMember" xlink:to="srt_WeightedAverageMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInput" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleValuationTechniqueExtensibleList" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleValuationTechniqueExtensibleList" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleValuationTechniqueExtensibleList" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleMeasurementInputExtensibleList" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInputExtensibleList" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleMeasurementInputExtensibleList" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsFairValueLevel3OnRecurringBasisDetails" xlink:type="extended" xlink:title="41104 - Disclosure - FAIR VALUE MEASUREMENTS - Fair Value Level 3 on recurring basis (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis" xlink:label="us-gaap_DerivativeInstrumentRiskAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_DerivativeInstrumentRiskAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain" xlink:label="us-gaap_DerivativeContractTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DerivativeInstrumentRiskAxis" xlink:to="us-gaap_DerivativeContractTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateLockCommitmentsMember" xlink:label="us-gaap_InterestRateLockCommitmentsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_InterestRateLockCommitmentsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForwardContractsMember" xlink:label="us-gaap_ForwardContractsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_DerivativeContractTypeDomain" xlink:to="us-gaap_ForwardContractsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsFairValueByBalanceSheetGroupingDetails" xlink:type="extended" xlink:title="41105 - Disclosure - FAIR VALUE MEASUREMENTS - Fair Value By Balance Sheet Grouping (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueByBalanceSheetGroupingTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_CarryingReportedAmountFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueByBalanceSheetGroupingTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueByBalanceSheetGroupingTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="us-gaap_FairValueByBalanceSheetGroupingTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:label="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CashDueFromBanksAndInterestBearingDepositsAtOtherFinancialInstitutionsFairValueDisclosure" xlink:label="fsbw_CashDueFromBanksAndInterestBearingDepositsAtOtherFinancialInstitutionsFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="fsbw_CashDueFromBanksAndInterestBearingDepositsAtOtherFinancialInstitutionsFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CertificatesOfDepositAtCarryingValue" xlink:label="us-gaap_CertificatesOfDepositAtCarryingValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_CertificatesOfDepositAtCarryingValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansHeldForSaleFairValueDisclosure" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_LoansHeldForSaleFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure" xlink:label="us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_InvestmentInFederalHomeLoanBankStockFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ForwardTbaMortgageBackedSecuritiesCommitmentAssetFairValueDisclosure" xlink:label="fsbw_ForwardTbaMortgageBackedSecuritiesCommitmentAssetFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="fsbw_ForwardTbaMortgageBackedSecuritiesCommitmentAssetFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableFairValueDisclosure" xlink:label="us-gaap_LoansReceivableFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_LoansReceivableFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeAssets" xlink:label="us-gaap_DerivativeAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DerivativeAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_AccruedInterestReceivableFairValueDisclosure" xlink:label="fsbw_AccruedInterestReceivableFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="fsbw_AccruedInterestReceivableFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" xlink:label="us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="us-gaap_LoansAndLeasesReceivableGrossCarryingAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MortgageCommercialAndConsumerServicingRightsFairValueDisclosure" xlink:label="fsbw_MortgageCommercialAndConsumerServicingRightsFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="fsbw_MortgageCommercialAndConsumerServicingRightsFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_InterestRateLockWithCustomersFairValue" xlink:label="fsbw_InterestRateLockWithCustomersFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="fsbw_InterestRateLockWithCustomersFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MandatoryAndBestEffortForwardCommitmentAssetWithInvestorsFairValueDisclosure" xlink:label="fsbw_MandatoryAndBestEffortForwardCommitmentAssetWithInvestorsFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:to="fsbw_MandatoryAndBestEffortForwardCommitmentAssetWithInvestorsFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:label="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:to="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepositsFairValueDisclosure" xlink:label="us-gaap_DepositsFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DepositsFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFairValue" xlink:label="us-gaap_DebtInstrumentFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DebtInstrumentFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisSubordinatedDebtObligations" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesFairValueDisclosure" xlink:label="us-gaap_AccruedLiabilitiesFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_AccruedLiabilitiesFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_MandatoryAndBestEffortForwardCommitmentsWithInvestorsAtFairValue" xlink:label="fsbw_MandatoryAndBestEffortForwardCommitmentsWithInvestorsAtFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract" xlink:to="fsbw_MandatoryAndBestEffortForwardCommitmentsWithInvestorsAtFairValue" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureFairValueMeasurementsNarrativeDetails" xlink:type="extended" xlink:title="41106 - Disclosure - FAIR VALUE MEASUREMENTS - Narrative (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResidentialMortgageMember" xlink:label="us-gaap_ResidentialMortgageMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ResidentialMortgageMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsNonrecurringMember" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsNonrecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansReceivableFairValueDisclosure" xlink:label="us-gaap_LoansReceivableFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_LoansReceivableFairValueDisclosure" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" xlink:label="us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountAsset" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_IncreaseDecreaseInFairValueOfLoansReceivable" xlink:label="fsbw_IncreaseDecreaseInFairValueOfLoansReceivable" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="fsbw_IncreaseDecreaseInFairValueOfLoansReceivable" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="us-gaap_AssetsFairValueDisclosure" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="us-gaap_AssetsFairValueDisclosure" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureStockBasedCompensationNarrativeDetails" xlink:type="extended" xlink:title="41301 - Disclosure - STOCK-BASED COMPENSATION - Narrative (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingAxis" xlink:label="us-gaap_VestingAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_VestingAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain" xlink:label="us-gaap_VestingDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_VestingAxis" xlink:to="us-gaap_VestingDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheOneMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheOneMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheTwoMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheTwoMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember" xlink:label="us-gaap_ShareBasedCompensationAwardTrancheThreeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_VestingDomain" xlink:to="us-gaap_ShareBasedCompensationAwardTrancheThreeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedPaymentArrangementTrancheFiveMember" xlink:label="fsbw_ShareBasedPaymentArrangementTrancheFiveMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_VestingDomain" xlink:to="fsbw_ShareBasedPaymentArrangementTrancheFiveMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_EquityIncentivePlan2018Member" xlink:label="fsbw_EquityIncentivePlan2018Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="fsbw_EquityIncentivePlan2018Member" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockOptionMember" xlink:label="us-gaap_StockOptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_StockOptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_EquityOptionAndRestrictedStockMember" xlink:label="fsbw_EquityOptionAndRestrictedStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="fsbw_EquityOptionAndRestrictedStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_TitleOfIndividualAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_IndependentDirectorMember" xlink:label="fsbw_IndependentDirectorMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="fsbw_IndependentDirectorMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DirectorExcludingCeoMember" xlink:label="fsbw_DirectorExcludingCeoMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="fsbw_DirectorExcludingCeoMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OfficersAndEmployeesMember" xlink:label="fsbw_OfficersAndEmployeesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="fsbw_OfficersAndEmployeesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage" xlink:label="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPercentage" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureStockBasedCompensationStockOptionActivityDetails" xlink:type="extended" xlink:title="41302 - Disclosure - STOCK-BASED COMPENSATION - Stock Option Activity (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_EquityIncentivePlan2018Member" xlink:label="fsbw_EquityIncentivePlan2018Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="fsbw_EquityIncentivePlan2018Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockOptionMember" xlink:label="us-gaap_StockOptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_StockOptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedForfeitureRate" xlink:label="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedForfeitureRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedForfeitureRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedForfeitureRateOverContractualTerm" xlink:label="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedForfeitureRateOverContractualTerm" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedForfeitureRateOverContractualTerm" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageRemainingContractualTermAbstract" xlink:label="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageRemainingContractualTermAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageRemainingContractualTermAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTerm" xlink:label="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTerm" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageRemainingContractualTermAbstract" xlink:to="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTerm" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageRemainingContractualTermAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageRemainingContractualTermAbstract" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" xlink:label="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="fsbw_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAggregateIntrinsicValueAbstract" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureStockBasedCompensationRestrictedStockAwardsDetails" xlink:type="extended" xlink:title="41303 - Disclosure - STOCK-BASED COMPENSATION - Restricted Stock Awards (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_EquityIncentivePlan2018Member" xlink:label="fsbw_EquityIncentivePlan2018Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="fsbw_EquityIncentivePlan2018Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_TitleOfIndividualAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_TitleOfIndividualAxis" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_IndependentDirectorMember" xlink:label="fsbw_IndependentDirectorMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="fsbw_IndependentDirectorMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DirectorExcludingCeoMember" xlink:label="fsbw_DirectorExcludingCeoMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="fsbw_DirectorExcludingCeoMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_OfficersAndEmployeesMember" xlink:label="fsbw_OfficersAndEmployeesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:to="fsbw_OfficersAndEmployeesMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember" xlink:label="us-gaap_RestrictedStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureRegulatoryCapitalNarrativeDetails" xlink:type="extended" xlink:title="41401 - Disclosure - REGULATORY CAPITAL - (Narrative) (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:label="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:to="srt_ConsolidatedEntitiesAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FirstSecurityBankMember" xlink:label="fsbw_FirstSecurityBankMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="fsbw_FirstSecurityBankMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:label="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalToAverageAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalToAverageAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1Capital" xlink:label="fsbw_CommonEquityTier1Capital" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1Capital" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalToRiskWeightedAssets" xlink:label="us-gaap_CapitalToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_CapitalToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1CapitalRatio" xlink:label="fsbw_CommonEquityTier1CapitalRatio" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1CapitalRatio" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureRegulatoryCapitalComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsDetails" xlink:type="extended" xlink:title="41402 - Disclosure - REGULATORY CAPITAL - Compliance with Regulatory Capital Requirements under Banking Regulations (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:label="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="srt_ConsolidatedEntitiesAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:to="srt_ConsolidatedEntitiesAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="srt_ConsolidatedEntitiesDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ConsolidatedEntitiesAxis" xlink:to="srt_ConsolidatedEntitiesDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FirstSecurityBankMember" xlink:label="fsbw_FirstSecurityBankMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ConsolidatedEntitiesDomain" xlink:to="fsbw_FirstSecurityBankMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:label="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_TotalRiskBasedCapital" xlink:label="fsbw_TotalRiskBasedCapital" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_TotalRiskBasedCapital" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalToRiskWeightedAssets" xlink:label="us-gaap_CapitalToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_CapitalToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_CapitalRequiredForCapitalAdequacy" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_CapitalRequiredForCapitalAdequacy" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:label="us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" xlink:label="fsbw_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CapitalRequiredForCapitalAdequacyWithCapitalBuffer" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CapitalRequiredForCapitalAdequacyWithCapitalBufferToRiskWeightedAssets" xlink:label="fsbw_CapitalRequiredForCapitalAdequacyWithCapitalBufferToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CapitalRequiredForCapitalAdequacyWithCapitalBufferToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_CapitalRequiredToBeWellCapitalized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_CapitalRequiredToBeWellCapitalized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:label="us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapital" xlink:label="us-gaap_TierOneRiskBasedCapital" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapital" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_TierOneRiskBasedMinimumCapitalAdequacyWithCapitalBuffer" xlink:label="fsbw_TierOneRiskBasedMinimumCapitalAdequacyWithCapitalBuffer" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_TierOneRiskBasedMinimumCapitalAdequacyWithCapitalBuffer" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_TierOneRiskBasedCapitalRequiredForCapitalAdequacyWithCapitalBufferToRiskWeightedAssets" xlink:label="fsbw_TierOneRiskBasedCapitalRequiredForCapitalAdequacyWithCapitalBufferToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_TierOneRiskBasedCapitalRequiredForCapitalAdequacyWithCapitalBufferToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:label="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapital" xlink:label="us-gaap_TierOneLeverageCapital" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapital" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalToAverageAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalToAverageAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:label="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="21" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:label="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="22" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" xlink:label="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="23" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1Capital" xlink:label="fsbw_CommonEquityTier1Capital" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="24" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1Capital" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1CapitalRatio" xlink:label="fsbw_CommonEquityTier1CapitalRatio" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="25" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1CapitalRatio" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1CapitalRequiredForCapitalAdequacy" xlink:label="fsbw_CommonEquityTier1CapitalRequiredForCapitalAdequacy" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="26" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1CapitalRequiredForCapitalAdequacy" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1CapitalRequiredForCapitalAdequacyPercent" xlink:label="fsbw_CommonEquityTier1CapitalRequiredForCapitalAdequacyPercent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="27" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1CapitalRequiredForCapitalAdequacyPercent" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_TierOneCommonEquityCapitalMinimumCapitalAdequacyWithCapitalBuffer" xlink:label="fsbw_TierOneCommonEquityCapitalMinimumCapitalAdequacyWithCapitalBuffer" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="28" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_TierOneCommonEquityCapitalMinimumCapitalAdequacyWithCapitalBuffer" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTierOneRiskBasedCapitalRequiredForMinimumCapitalAdequacyWithCapitalBufferPurposesRiskWeightedAssets" xlink:label="fsbw_CommonEquityTierOneRiskBasedCapitalRequiredForMinimumCapitalAdequacyWithCapitalBufferPurposesRiskWeightedAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="29" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTierOneRiskBasedCapitalRequiredForMinimumCapitalAdequacyWithCapitalBufferPurposesRiskWeightedAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1CapitalRequiredToBeWellCapitalized" xlink:label="fsbw_CommonEquityTier1CapitalRequiredToBeWellCapitalized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="30" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1CapitalRequiredToBeWellCapitalized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommonEquityTier1CapitalRequiredToBeWellCapitalizedPercent" xlink:label="fsbw_CommonEquityTier1CapitalRequiredToBeWellCapitalizedPercent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="31" xlink:from="us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="fsbw_CommonEquityTier1CapitalRequiredToBeWellCapitalizedPercent" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureBusinessSegmentsSegmentFinancialResultsDetails" xlink:type="extended" xlink:title="41501 - Disclosure - BUSINESS SEGMENTS - Segment Financial Results (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="us-gaap_StatementBusinessSegmentsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_SegmentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_HomeLendingMember" xlink:label="fsbw_HomeLendingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SegmentDomain" xlink:to="fsbw_HomeLendingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_CommercialAndConsumerBankingMember" xlink:label="fsbw_CommercialAndConsumerBankingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentDomain" xlink:to="fsbw_CommercialAndConsumerBankingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="us-gaap_SegmentReportingInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_InterestIncomeExpenseNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="us-gaap_ProvisionForLoanAndLeaseLosses" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_ProvisionForLoanAndLeaseLosses" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NoninterestIncome" xlink:label="us-gaap_NoninterestIncome" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_NoninterestIncome" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NoninterestExpense" xlink:label="us-gaap_NoninterestExpense" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_NoninterestExpense" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_NetIncomeLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAverageOutstanding" xlink:label="us-gaap_AssetsAverageOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_AssetsAverageOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityNumberOfEmployees" xlink:label="dei_EntityNumberOfEmployees" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="dei_EntityNumberOfEmployees" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureBusinessSegmentsNarrativeDetails" xlink:type="extended" xlink:title="41502 - Disclosure - BUSINESS SEGMENTS - Narrative (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="srt_ProductOrServiceAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_RetailDepositMember" xlink:label="fsbw_RetailDepositMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ProductsAndServicesDomain" xlink:to="fsbw_RetailDepositMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="srt_StatementGeographicalAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_StatementGeographicalAxis" xlink:to="srt_SegmentGeographicalDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_PacificNorthwestMember" xlink:label="fsbw_PacificNorthwestMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_SegmentGeographicalDomain" xlink:to="fsbw_PacificNorthwestMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="us-gaap_SegmentReportingInformationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfOperatingSegments" xlink:label="us-gaap_NumberOfOperatingSegments" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_NumberOfOperatingSegments" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfBankBranches" xlink:label="fsbw_NumberOfBankBranches" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="fsbw_NumberOfBankBranches" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfBankOwnedBranchesAcquired" xlink:label="fsbw_NumberOfBankOwnedBranchesAcquired" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="fsbw_NumberOfBankOwnedBranchesAcquired" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureGoodwillAndOtherIntangibleAssetsDetails" xlink:type="extended" xlink:title="41601 - Disclosure - GOODWILL AND OTHER INTANGIBLE ASSETS (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="us-gaap_BusinessAcquisitionAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_AnchorBancorpMember" xlink:label="fsbw_AnchorBancorpMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fsbw_AnchorBancorpMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_BankOfAmericaMember" xlink:label="fsbw_BankOfAmericaMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fsbw_BankOfAmericaMember" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_ColumbiaStateBankMember" xlink:label="fsbw_ColumbiaStateBankMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="fsbw_ColumbiaStateBankMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_Goodwill" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillImpairmentLoss" xlink:label="us-gaap_GoodwillImpairmentLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_GoodwillImpairmentLoss" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="us-gaap_AmortizationOfIntangibleAssets" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_AmortizationOfIntangibleAssets" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FiniteLivedIntangibleAssetsAcquiredGross" xlink:label="fsbw_FiniteLivedIntangibleAssetsAcquiredGross" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="fsbw_FiniteLivedIntangibleAssetsAcquiredGross" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1" xlink:label="us-gaap_FinitelivedIntangibleAssetsAcquired1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FinitelivedIntangibleAssetsAcquired1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_NumberOfRetailBankBranchesAcquired" xlink:label="fsbw_NumberOfRetailBankBranchesAcquired" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="fsbw_NumberOfRetailBankBranchesAcquired" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:label="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFour" xlink:label="fsbw_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFour" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract" xlink:to="fsbw_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFour" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.fsbwa.com/role/DisclosureRevenueFromContractsWithCustomersDetails" xlink:type="extended" xlink:title="41701 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:label="srt_ProductOrServiceAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="srt_ProductOrServiceAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:label="srt_ProductsAndServicesDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DebitCardInterchangeFeesMember" xlink:label="fsbw_DebitCardInterchangeFeesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ProductsAndServicesDomain" xlink:to="fsbw_DebitCardInterchangeFeesMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="fsbw-20230630.xsd#fsbw_DepositServiceAndAccountMaintenanceFeesMember" xlink:label="fsbw_DepositServiceAndAccountMaintenanceFeesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_ProductsAndServicesDomain" xlink:to="fsbw_DepositServiceAndAccountMaintenanceFeesMember" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NoninterestIncomeAbstract" xlink:label="us-gaap_NoninterestIncomeAbstract" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NoninterestIncomeAbstract" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueNotFromContractWithCustomerExcludingInterestIncome" xlink:label="us-gaap_RevenueNotFromContractWithCustomerExcludingInterestIncome" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_RevenueNotFromContractWithCustomerExcludingInterestIncome" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NoninterestIncome" xlink:label="us-gaap_NoninterestIncome" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_NoninterestIncomeAbstract" xlink:to="us-gaap_NoninterestIncome" priority="1" use="optional" />
  </definitionLink>
</link:linkbase>
