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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,
 R9Me4HQxn1tOhhWt5MR4z5UoOWGrEtvhJZNBYVgbhatAoFpz7bGUo9khJvf71b5k
 97WhSuUx2fLKPuOEEomT+g==

<SEC-DOCUMENT>0001226898-09-000001.txt : 20090203
<SEC-HEADER>0001226898-09-000001.hdr.sgml : 20090203
<ACCEPTANCE-DATETIME>20090203192216
ACCESSION NUMBER:		0001226898-09-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20090202
FILED AS OF DATE:		20090203
DATE AS OF CHANGE:		20090203

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BERDAHL ROBERT M
		CENTRAL INDEX KEY:			0001226898

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-12933
		FILM NUMBER:		09566481

	MAIL ADDRESS:	
		STREET 1:		2400 HEARST AVE
		CITY:			BERKELEY
		STATE:			CA
		ZIP:			94709

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			LAM RESEARCH CORP
		CENTRAL INDEX KEY:			0000707549
		STANDARD INDUSTRIAL CLASSIFICATION:	SPECIAL INDUSTRY MACHINERY, NEC [3559]
		IRS NUMBER:				942634797
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		4650 CUSHING BLVD
		CITY:			FREMONT
		STATE:			CA
		ZIP:			94538
		BUSINESS PHONE:		5106590200

	MAIL ADDRESS:	
		STREET 1:		4650 CUSHING PARKWAY
		CITY:			FREMONT
		STATE:			CA
		ZIP:			94538
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-02-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000707549</issuerCik>
        <issuerName>LAM RESEARCH CORP</issuerName>
        <issuerTradingSymbol>LRCX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001226898</rptOwnerCik>
            <rptOwnerName>BERDAHL ROBERT M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2400 HEARST AVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BERKELEY</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94709</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-02-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8130</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17948</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>Kym Hall by Power of Attorney</signatureName>
        <signatureDate>2009-02-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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