-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Ow64V5O9Jc8dWT+VzzjDKHjlICgEA4WGEFP/76sWFDfz2f5KujszRuBkJMK0ZbGE
 F2Cl//tGaCXnjOfhlHn7qQ==

<SEC-DOCUMENT>0000950138-06-000628.txt : 20060816
<SEC-HEADER>0000950138-06-000628.hdr.sgml : 20060816
<ACCEPTANCE-DATETIME>20060816141741
ACCESSION NUMBER:		0000950138-06-000628
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060814
FILED AS OF DATE:		20060816
DATE AS OF CHANGE:		20060816

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:		90 INDUSTRIAL WAY
		CITY:			WILMINGTON
		STATE:			MA
		ZIP:			01887
		BUSINESS PHONE:		978-284-4000

	MAIL ADDRESS:	
		STREET 1:		90 INDUSTRIAL WAY
		CITY:			WILMINGTON
		STATE:			MA
		ZIP:			01887

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			EMERSON ELECTRIC CO
		CENTRAL INDEX KEY:			0000032604
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRONIC & OTHER ELECTRICAL EQUIPMENT (NO COMPUTER EQUIP) [3600]
		STATE OF INCORPORATION:			MO
		FISCAL YEAR END:			0930

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-23621
		FILM NUMBER:		061037843

	BUSINESS ADDRESS:	
		STREET 1:		8000 W FLORISSANT AVE
		STREET 2:		P O BOX 4100
		CITY:			ST LOUIS
		STATE:			MO
		ZIP:			63136
		BUSINESS PHONE:		3145532000

	MAIL ADDRESS:	
		STREET 1:		8000 W. FLORISSANT
		STREET 2:		P.O. BOX 4100
		CITY:			ST LOUIS
		STATE:			MO
		ZIP:			63136

	FORMER NAME:	
		FORMER CONFORMED NAME:	EMERSON ELECTRIC MANUFACTUING CO
		DATE OF NAME CHANGE:	19730710
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4_081506ex.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-08-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000032604</rptOwnerCik>
            <rptOwnerName>EMERSON ELECTRIC CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>8000 W. FLORISSANT AVE.</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ST LOUIS</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63136</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>45820</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.1337</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4662137</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Through a subsidiary</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>71800</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.932</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4590337</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Through a subsidiary</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1065182</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The sales were effected in multiple transactions, at varying prices, on August 14, 2006, as follows and as described in
 Footnote 2 below:  12,700 shares at $19.00; 1,500 at $19.01; 1,200 at $19.02; 900 at $19.03; 500 at $19.04; 800 at $19.05;
 900 at $19.06; 1,600 at $19.07; 1,300 at $19.08; 1,500 at $19.09; 1,900 at $19.10; 1,000 at $19.11; 1,200 at $19.12; 600 at
 $19.13; 800 at $19.14; 1,000 at $19.15; 300 at $19.16; 600 at $19.17; 300 at $19.18; 700 at $19.19; 300 at $19.20; 400 at
 $19.21; 400 at $19.22; 806 at $19.23; and 887 at $19.24.</footnote>
        <footnote id="F2">This footnote sets forth additional detail with respect to the transactions described in Footnote 1, as follows:  2,107
 shares at $19.25; 800 at $19.26; 300 at $19.27; 1,200 at $19.28; 500 at $19.29; 246 at $19.30; 174 at $19.31; 200 at $19.32;
 422 at $19.33; 600 at $19.34; 1,000 at $19.35; 678 at $19.36; 300 at $19.37; 200 at $19.38; 500 at $19.39; 1,100 at $19.40;
 300 at $19.41; 700 at $19.42; 200 at $19.44; and 200 at $19.46. The weighted average sales price for these transactions was
 $19.1337 per share.</footnote>
        <footnote id="F3">The sales were effected in multiple transactions, at varying prices, on August 15, 2006, as follows and as described in
 Footnotes 4 and 5 below:  155 shares at $19.12; 45 at $19.13; 200 at $19.15; 100 at $19.16; 116 at $19.29; 600 at $19.37;
 400 at $19.38; 200 at $19.39; 188 at $19.40; 200 at $19.41; 100 at $19.42; 100 at $19.43; 200 at $19.45; 100 at $19.46; 400
 at $19.47; 100 at $19.48; 600 at $19.49; 300 at $19.50; 400 at $19.51; 400 at $19.52; 100 at $19.53; 600 at $19.54; 200 at
 $19.55; 400 at $19.56; 200 at $19.59; and 100 at $19.62.</footnote>
        <footnote id="F4">This footnote sets forth additional detail with respect to the transactions described in Footnote 3, as follows:  200 shares
 at $19.64; 200 at $19.67; 200 at $19.68; 500 at $19.69; 700 at $19.70; 100 at $19.71; 700 at $19.72; 400 at $19.73; 300 at
 $19.74; 200 at $19.75; 200 at $19.76; 200 at $19.77; 800 at $19.78; 800 at $19.79; 400 at $19.80; 900 at $19.81; 300 at
 $19.82; 1,000 at $19.83; 800 at $19.84; 955 at $19.85; 2,400 at $19.86; 1,300 at $19.87; 1,926 at $19.88; 2,300 at $19.89;
 and 3,900 at $19.90.</footnote>
        <footnote id="F5">This footnote sets forth additional detail with respect to the transactions described in Footnotes 3 and 4, as follows:
 3,850 shares at $19.91; 1,683 at $19.92; 2,117 at $19.93; 2,248 at $19.94; 4,291 at $19.95; 2,952 at $19.96; 1,909 at
 $19.97; 400 at $19.98; 200 at $19.99; 677 at $20.00; 1,088 at $20.01; 700 at $20.02; 200 at $20.03; 1,000 at $20.04; 400 at
 $20.05; 1,000 at $20.06; 1,000 at $20.07; 300 at $20.08; 200 at $20.09; 500 at $20.10; 400 at $20.11; 100 at $20.12; 259 at
 $20.14; 2,041 at $20.15; 900 at $20.16; 1,900 at $20.17; 2,600 at $20.18; 3,300 at $20.19; 2,300 at $20.20; 200 at $20.21;
 200 at $20.22; 600 at $20.23; and 2,100 at $20.24. The weighted average sales price for these transactions was $19.932 per
 share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Timothy G. Westman,  Assistant Secretary</signatureName>
        <signatureDate>2006-08-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----