-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Fa9x3ihXjpU6ztPBLqkCxwSl6nW7+CV0FuUzj99fsh+UL+MPUpHeqgtBAu0V9cMA
 FAfuAUsDaCbRxkjL66S63g==

<SEC-DOCUMENT>0001102934-03-000048.txt : 20030924
<SEC-HEADER>0001102934-03-000048.hdr.sgml : 20030924
<ACCEPTANCE-DATETIME>20030924163213
ACCESSION NUMBER:		0001102934-03-000048
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20030923
FILED AS OF DATE:		20030924

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:			SKATES RONALD L
		CENTRAL INDEX KEY:			0001189841

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30205
		FILM NUMBER:		03908384

	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>c0001189841d20030924f4f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<ownershipDocument><schemaVersion>X0201</schemaVersion>    <documentType>4</documentType><periodOfReport>2003-09-23</periodOfReport><notSubjectToSection16>0</notSubjectToSection16><issuer><issuerCik>0001102934</issuerCik><issuerName>CABOT MICROELECTRONICS CORP</issuerName>        <issuerTradingSymbol>CCMP</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId><rptOwnerCik>0001189841</rptOwnerCik><rptOwnerName>SKATES RONALD L</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>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle></officerTitle><otherText></otherText></reportingOwnerRelationship>
</reportingOwner><nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>2560</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeHolding></nonDerivativeTable><derivativeTable><derivativeHolding><securityTitle><value>Stock Options (Right to buy)</value></securityTitle><conversionOrExercisePrice><value>20</value></conversionOrExercisePrice><exerciseDate><value>2001-04-04</value></exerciseDate><expirationDate><value>2005-04-04</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>20000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><va
lue>20000</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>38.34</value></conversionOrExercisePrice><exerciseDate><value>2004-03-11</value></exerciseDate><expirationDate><value>2013-03-11</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>7500</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>7500</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>46.875</value></conversionOrExercisePrice><exerciseDate><value>2002-03-13</value></exerciseDate><expirationDate><value>2008-03-13</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>7500</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>7500</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>65.73</value></conversionOrExercisePrice><exerciseDate><value>2002-03-12</value></exercise
Date><expirationDate><value>2012-03-12</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>7500</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>7500</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Phantom Stock</value></securityTitle><conversionOrExercisePrice><value>50.95</value></conversionOrExercisePrice><exerciseDate><value>2003-06-18</value></exerciseDate><expirationDate><value>2003-06-17</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>1513.9321</value></underlyingSecurityShares></underlyingSe
curity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1513.9321</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeHolding><derivativeTransaction><securityTitle><value>Phantom Stock</value></securityTitle><conversionOrExercisePrice><value>59.05</value></conversionOrExercisePrice><transactionDate><value>2003-09-23</value></transactionDate><deemedExecutionDate></deemedExecutionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>J</transactionCode><equitySwapInvolved>0</equitySwapInvolved><footnoteId id="F2"/></transactionCoding><transactionAmounts><transactionShares><value>50.8044</value></transactionShares><transactionPricePerShare><value>0</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts>
<exerciseDate><value>2003-09-23</value></exerciseDate><expirationDate><value>2013-09-23</value><footnoteId id="F3"/></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>50.8044</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>50.8044</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">Cabot Corporation (NYSE: CBT) spun off its 80.5 percent equity interest in CCMP by distributing a special dividend to CBT common stockholders of record as of the close of business on 9/13/2000.  The tax-free distribution took place on 9/29/2000.  Mr. Skates received 560 shares of CCMP as a result of this special dividend.</fo
otnote><footnote id="F2">Rights to acquire shares pursuant to Directors' Deferred Compensation Plan adopted March 12, 2001 as amended June 17, 2003.</footnote><footnote id="F3">Rights to aquire shares pursuant to Directors' Deferred Compensation Plan are already earned.</footnote></footnotes><ownerSignature><signatureName>Ronald L Skates</signatureName><signatureDate>2003-09-24</signatureDate></ownerSignature></ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----