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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 k5C438aRK6iPPivTUcbBqQ==

<SEC-DOCUMENT>0001210985-05-000005.txt : 20050921
<SEC-HEADER>0001210985-05-000005.hdr.sgml : 20050921
<ACCEPTANCE-DATETIME>20050921191039
ACCESSION NUMBER:		0001210985-05-000005
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050916
FILED AS OF DATE:		20050921
DATE AS OF CHANGE:		20050921

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			INTEGRATED CIRCUIT SYSTEMS INC
		CENTRAL INDEX KEY:			0000874689
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				232000174
		STATE OF INCORPORATION:			PA
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		2435 BLVD OF THE GENERALS
		CITY:			NORRISTOWN
		STATE:			PA
		ZIP:			19403
		BUSINESS PHONE:		6106305300

	MAIL ADDRESS:	
		STREET 1:		2435 BLVD OF THE GENERALS
		CITY:			NORRISTOWN
		STATE:			PA
		ZIP:			19403

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			EGGEBRECHT LEWIS C
		CENTRAL INDEX KEY:			0001213489

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-19299
		FILM NUMBER:		051096820

	BUSINESS ADDRESS:	
		STREET 1:		2590 BIG BEAR CIRCLE
		CITY:			SEDALIA
		STATE:			CO
		ZIP:			80135
		BUSINESS PHONE:		4804632004

	MAIL ADDRESS:	
		STREET 1:		C/O INTEGRATED DEVICE TECHNOLOGY, INC.
		STREET 2:		6024 SILVER CREEK VALLEY ROAD
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95138
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-09-16</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000874689</issuerCik>
        <issuerName>INTEGRATED CIRCUIT SYSTEMS INC</issuerName>
        <issuerTradingSymbol>ICST</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001213489</rptOwnerCik>
            <rptOwnerName>EGGEBRECHT LEWIS C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O INTEGRATED DEVICE TECHNOLOGY, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>6024 SILVER CREEK VALLEY ROAD</rptOwnerStreet2>
            <rptOwnerCity>SAN JOSE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95138</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Former Director</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-09-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>103721</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Right to Buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>32.86</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-09-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2004-10-29</value>
            </exerciseDate>
            <expirationDate>
                <value>2013-10-29</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>8000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Right to Buy</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>22.35</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-09-16</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>24000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-08-28</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-08-28</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>24000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Disposed of pursuant to the merger agreement (&quot;Agreement&quot;) between issuer, Integrated Device Technology, Inc. (&quot;IDT&quot;) and Colonial Merger Sub I, Inc. for approximately 134,837 shares of IDT common stock having a market value of $11.23/share on the effective date of the merger, plus approximately $751,977.</footnote>
        <footnote id="F2">The option, whether or not exercisable, was cancelled in the merger in exchange for a cash payment of $0 , representing the difference between the exercise price of the option and the &quot;Total Purchase Price Per Share&quot; as defined in the Agreement, which on the effective date of merger was $21.62/share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Leslie Fleischer</signatureName>
        <signatureDate>2005-09-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----