-----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,
 BPX4SnZrqe1HxabdaI6lHigW9j5d3EMp/VFbGptSTRyE77bAwyske9+MotZCFocC
 44sHH3hwtaBchiZyAvk9Eg==

<SEC-DOCUMENT>0001102934-03-000067.txt : 20031212
<SEC-HEADER>0001102934-03-000067.hdr.sgml : 20031212
<ACCEPTANCE-DATETIME>20031212105807
ACCESSION NUMBER:		0001102934-03-000067
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20031211
FILED AS OF DATE:		20031212

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CABOT MICROELECTRONICS CORP
		CENTRAL INDEX KEY:			0001102934
		STANDARD INDUSTRIAL CLASSIFICATION:	ABRASIVE ASBESTOS & MISC NONMETALLIC MINERAL PRODUCTS [3290]
		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:			SMITH STEPHEN R
		CENTRAL INDEX KEY:			0001189882

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30205
		FILM NUMBER:		031050928

	BUSINESS ADDRESS:	
		STREET 1:		870 N COMMONS DR
		CITY:			AURORA
		STATE:			IL
		ZIP:			60504
		BUSINESS PHONE:		6303755461

	MAIL ADDRESS:	
		STREET 1:		870 N COMMONS DR
		CITY:			AURORA
		STATE:			IL
		ZIP:			60504
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>c0001189882d20031212f4f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
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<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-12-11</periodOfReport><notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0001102934</issuerCik>
        <issuerName>CABOT MICROELECTRONICS CORP</issuerName>
        <issuerTradingSymbol>CCMP</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001189882</rptOwnerCik>
            <rptOwnerName>SMITH STEPHEN R</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, Marketing and</officerTitle><otherText></otherText></reportingOwnerRelationship></reportingOwner><nonDerivativeTable></nonDerivativeTable><derivativeTable><derivativeTransaction><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>48.91</value></conversionOrExercisePrice><transactionDate><value>2003-12-11</value></transactionDate><deemedExecutionDate></deemedExecutionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>60000</value><footnoteId id="F1"/></transactionShares><transactionPricePerShare><value>0</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><valu
e>2004-12-11</value></exerciseDate><expirationDate><value>2013-12-11</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>60000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>60000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeHolding><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>49.8</value></conversionOrExercisePrice><exerciseDate><value>2003-05-01</value></exerciseDate><expirationDate><value>2012-05-01</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>15000</v
alue></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>15000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>51.37</value></conversionOrExercisePrice><exerciseDate><value>2003-12-11</value></exerciseDate><expirationDate><value>2012-12-11</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>57000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>57000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><v
alue>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>64.66</value></conversionOrExercisePrice><exerciseDate><value>2001-10-29</value></exerciseDate><expirationDate><value>2008-10-29</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityValue><value>12000</value></underlyingSecurityValue></underlyingSecurity><postTransactionAmounts><valueOwnedFollowingTransaction><value>12000</value></valueOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeHolding></derivativeTable><footnotes><footnote id="F1">Vesting Schedule:
25% 12/11/04
25% 12/11/05
25% 12/11/06
25% 12/11/07</footnote></footnotes><ownerSignature><signatureName>Stephen R Smith</signatureName><signatureDate>2003-12-12</signatureDate></ownerSignature></ownershipDocument>

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