-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 v+tVMQGr7cawG1YsfeUF2w==

<SEC-DOCUMENT>0001102934-08-000115.txt : 20081211
<SEC-HEADER>0001102934-08-000115.hdr.sgml : 20081211
<ACCEPTANCE-DATETIME>20081211171943
ACCESSION NUMBER:		0001102934-08-000115
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20081210
FILED AS OF DATE:		20081211
DATE AS OF CHANGE:		20081211

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CABOT MICROELECTRONICS CORP
		CENTRAL INDEX KEY:			0001102934
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				364324765
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0930

	BUSINESS ADDRESS:	
		STREET 1:		870 NORTH COMMONS DRIVE
		CITY:			AURORA
		STATE:			IL
		ZIP:			60504
		BUSINESS PHONE:		6303755461

	MAIL ADDRESS:	
		STREET 1:		870 N COMMONS DR
		CITY:			AURORA
		STATE:			IL
		ZIP:			60504

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			JOHNSON WILLIAM S
		CENTRAL INDEX KEY:			0001223693

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30205
		FILM NUMBER:		081244219

	BUSINESS ADDRESS:	
		STREET 1:		870 N. COMMONS DR.
		STREET 2:		C/O CABOT MICROELECTRONICS
		CITY:			AURORA
		STATE:			IL
		ZIP:			60504
		BUSINESS PHONE:		6303755461

	MAIL ADDRESS:	
		STREET 1:		C/O CABOT MICROELECTRONICS
		STREET 2:		870 N. COMMONS DR
		CITY:			AURORA
		STATE:			IL
		ZIP:			60504
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-12-10</periodOfReport>

    <issuer>
        <issuerCik>0001102934</issuerCik>
        <issuerName>CABOT MICROELECTRONICS CORP</issuerName>
        <issuerTradingSymbol>CCMP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001223693</rptOwnerCik>
            <rptOwnerName>JOHNSON WILLIAM S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CABOT MICROELECTRONICS CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>870 COMMONS DRIVE</rptOwnerStreet2>
            <rptOwnerCity>AURORA</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60504</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President, CFO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-10</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>712</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>24.55</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>34616.179</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-12-10</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1425</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>24.55</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>36041.179</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>800</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents restricted shares purchased under the Issuer's Equity Incentive Plan pursuant to the Issuer's Deposit Share Program;  1,425 of such shares are Deposit Shares under the Program purchased at full value by the Participant that will vest on 12/10/2008, and 712 shares of such are Award Shares under the Program awarded to the Participant that will vest on 12/10/2011, subject to the satisfaction of certain conditions.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>H. Carol Bernstein</signatureName>
        <signatureDate>2008-12-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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