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      <filer>
        <filerCredentials>
          <cik>0001775435</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



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    <issuerInfo>
      <issuerCik>0001049502</issuerCik>
      <issuerName>MKS INSTRUMENTS INC</issuerName>
      <secFileNumber>000-23621</secFileNumber>
      <issuerAddress>
        <com:street1>2 TECH DRIVE</com:street1>
        <com:street2>SUITE 201</com:street2>
        <com:city>ANDOVER</com:city>
        <com:stateOrCountry>MA</com:stateOrCountry>
        <com:zipCode>01810</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>978-645-5500</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Burke Kathleen Flaherty</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Officer</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>Fidelity Brokerage Services LLC</name>
        <address>
          <com:street1>900 Salem St</com:street1>
          <com:city>Smithfield</com:city>
          <com:stateOrCountry>RI</com:stateOrCountry>
          <com:zipCode>02917</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>6186</noOfUnitsSold>
      <aggregateMarketValue>625304.01</aggregateMarketValue>
      <noOfUnitsOutstanding>66862788</noOfUnitsOutstanding>
      <approxSaleDate>08/07/2023</approxSaleDate>
      <securitiesExchangeName>NASDAQ</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>02/15/2021</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>4885</amountOfSecuritiesAcquired>
      <paymentDate>02/15/2021</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>05/28/2021</acquiredDate>
      <natureOfAcquisitionTransaction>ESPP Purchase</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>89</amountOfSecuritiesAcquired>
      <paymentDate>05/28/2021</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>10/28/2021</acquiredDate>
      <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>1212</amountOfSecuritiesAcquired>
      <paymentDate>10/28/2021</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <noticeSignature>
      <noticeDate>08/07/2023</noticeDate>
      <signature>/s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Kathleen F. Burke</signature>
    </noticeSignature>
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144
0001775435
XXXXXXXX
LIVE
0001049502
MKS INSTRUMENTS INC
000-23621
2 TECH DRIVE
SUITE 201
ANDOVER
MA
01810
978-645-5500
Burke Kathleen Flaherty
Officer
Common
Fidelity Brokerage Services LLC
900 Salem St
Smithfield
RI
02917
6186
625304.01
66862788
08/07/2023
NASDAQ
Common
02/15/2021
Restricted Stock Vesting
Issuer
N
4885
02/15/2021
Compensation
Common
05/28/2021
ESPP Purchase
Issuer
N
89
05/28/2021
Cash
Common
10/28/2021
Restricted Stock Vesting
Issuer
N
1212
10/28/2021
Compensation
Y
08/07/2023
/s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Kathleen F. Burke