<SEC-DOCUMENT>0001127602-21-014262.txt : 20210422
<SEC-HEADER>0001127602-21-014262.hdr.sgml : 20210422
<ACCEPTANCE-DATETIME>20210422150339
ACCESSION NUMBER:		0001127602-21-014262
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20210413
FILED AS OF DATE:		20210422
DATE AS OF CHANGE:		20210422

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Gitin Mark Milton
		CENTRAL INDEX KEY:			0001842711

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-23621
		FILM NUMBER:		21844467

	MAIL ADDRESS:	
		STREET 1:		MKS INSTRUMENTS, INC., 2 TECH DRIVE
		STREET 2:		SUITE 201
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MKS INSTRUMENTS INC
		CENTRAL INDEX KEY:			0001049502
		STANDARD INDUSTRIAL CLASSIFICATION:	INDUSTRIAL INSTRUMENTS FOR MEASUREMENT, DISPLAY, AND CONTROL [3823]
		IRS NUMBER:				042277512
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2 TECH DRIVE
		STREET 2:		SUITE 201
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810
		BUSINESS PHONE:		978-645-5500

	MAIL ADDRESS:	
		STREET 1:		2 TECH DRIVE
		STREET 2:		SUITE 201
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>form4a.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2021-04-13</periodOfReport>

    <dateOfOriginalSubmission>2021-04-14</dateOfOriginalSubmission>

    <issuer>
        <issuerCik>0001049502</issuerCik>
        <issuerName>MKS INSTRUMENTS INC</issuerName>
        <issuerTradingSymbol>MKSI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001842711</rptOwnerCik>
            <rptOwnerName>Gitin Mark Milton</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MKS INSTRUMENTS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2 TECH DRIVE, SUITE 201</rptOwnerStreet2>
            <rptOwnerCity>ANDOVER</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01810</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>SVP &amp; GM, L&amp;M Division</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-04-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>317</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>186.52</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4733.054</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person.</footnote>
        <footnote id="F2">The original Form 4 filed on April 14, 2021 (the &quot;Original Form 4&quot;), is hereby amended solely to correct an error in the number of shares of common stock of MKS Instruments, Inc. that were withheld from the reporting person for the payment of tax liabilities. Please note that the 70 additional shares that should have been reported as withheld for the payment of tax liabilities on the Original Form 4 were included in the reporting person's holdings in a subsequent Form 4 filed on April 21, 2021.  The reporting person will exclude these shares from the reporting person's holdings in future filings.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ M. Kathryn Rickards, attorney-in-fact</signatureName>
        <signatureDate>2021-04-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
