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  <headerData>
    <submissionType>144</submissionType>
    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001186476</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



    </filerInfo>
  </headerData>
  <formData>
    <issuerInfo>
      <issuerCik>0000937556</issuerCik>
      <issuerName>MASIMO CORP</issuerName>
      <secFileNumber>001-33642</secFileNumber>
      <issuerAddress>
        <com:street1>52 DISCOVERY</com:street1>
        <com:city>IRVINE</com:city>
        <com:stateOrCountry>CA</com:stateOrCountry>
        <com:zipCode>92618</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>949-297-7000</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>REYNOLDS CRAIG B</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Former Director</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>Charles Schwab &amp; Co., Inc.</name>
        <address>
          <com:street1>3000 Schwab Way,</com:street1>
          <com:city>Westlake</com:city>
          <com:stateOrCountry>TX</com:stateOrCountry>
          <com:zipCode>76262</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>16443</noOfUnitsSold>
      <aggregateMarketValue>2696652.00</aggregateMarketValue>
      <noOfUnitsOutstanding>54219116</noOfUnitsOutstanding>
      <approxSaleDate>05/13/2025</approxSaleDate>
      <securitiesExchangeName>NASDAQ</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>05/31/2018</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Lapse - See Remarks</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>MASIMO CORPORATION</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>16443</amountOfSecuritiesAcquired>
      <paymentDate>05/31/2018</paymentDate>
      <natureOfPayment>Equity Compensation</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>CRAIG B REYNOLDS</name>
        <address>
          <com:street1>52 DISCOVERY</com:street1>
          <com:city>IRVINE</com:city>
          <com:stateOrCountry>CA</com:stateOrCountry>
          <com:zipCode>92618</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>MASIMO CORP</securitiesClassTitle>
      <saleDate>03/14/2025</saleDate>
      <amountOfSecuritiesSold>2053</amountOfSecuritiesSold>
      <grossProceeds>341068.00</grossProceeds>
    </securitiesSoldInPast3Months>
    <remarks>Shares on this filing were acquired and paid for from 05/31/2018 through 04/29/2025.</remarks>
    <noticeSignature>
      <noticeDate>05/13/2025</noticeDate>
      <signature>CRAIG B REYNOLDS</signature>
    </noticeSignature>
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144
0001186476
XXXXXXXX
LIVE
0000937556
MASIMO CORP
001-33642
52 DISCOVERY
IRVINE
CA
92618
949-297-7000
REYNOLDS CRAIG B
Former Director
Common
Charles Schwab & Co., Inc.
3000 Schwab Way,
Westlake
TX
76262
16443
2696652.00
54219116
05/13/2025
NASDAQ
Common
05/31/2018
Restricted Stock Lapse - See Remarks
MASIMO CORPORATION
N
16443
05/31/2018
Equity Compensation
N
CRAIG B REYNOLDS
52 DISCOVERY
IRVINE
CA
92618
MASIMO CORP
03/14/2025
2053
341068.00
Shares on this filing were acquired and paid for from 05/31/2018 through 04/29/2025.
05/13/2025
CRAIG B REYNOLDS