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EXHIBIT 31.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, Thian Hoo Tan, certify that:



|1. |  | I have reviewed this quarterly report on Form 10-Q of Komag,
Incorporated;                                                                                                                                                                                                                                
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|2. |  | Based on my knowledge, this report does not contain any untrue statement
of a material fact or omit to state a material fact necessary to make the
statements made, in light of the circumstances under which such statements
were made, not misleading with respect to the period covered by this
report;
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|3. |  | Based on my knowledge, the financial statements and other financial
information included in this report fairly present, in all material
respects, the financial condition and results of operations and cash flows
of the registrant as of, and for, the periods presented in this report;                
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|4. |  | The registrants other certifying officer and I are responsible for
establishing and maintaining disclosure controls and procedures (as
defined in Exchange Act Rules 13a  15(e) and 15d  15(e)) for the
registrant and have:                                                                           



| | a) |  | Designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the
registrant, including its consolidated subsidiaries, is made known to
us by others within those entities, particularly during the period in
which this report is being prepared;         
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| | b) |  | Evaluated the effectiveness of the registrants disclosure controls
and procedures and presented in this report our conclusions about the
effectiveness of the disclosure controls and procedures, as of the end
of the period covered by this report based on such evaluation; and                                                                                                    
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| | c) |  | Disclosed in this report any change in the registrants internal
control over financial reporting that occurred during the registrants
most recent fiscal quarter (the registrants fourth fiscal quarter in
the case of an annual report) that has materially affected, or is
reasonably likely to materially affect, the registrants internal
control over financial reporting; and



|5. |  | The registrants other certifying officer and I have disclosed, based on
our most recent evaluation of internal control over financial reporting,
to the registrants auditors and the audit committee of the registrants
board of directors:
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| | a) |  | All significant deficiencies and material weaknesses in the design
or operation of internal control over financial reporting which are
reasonably likely to adversely affect the registrants ability to
record, process, summarize, and report financial information; and
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| | b) |  | Any fraud, whether or not material, that involves management or
other employees who have a significant role in the registrants
internal control over financial reporting.                                                                                                

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|DATE: |  | July 31, 2003 |  | BY:                                   |  | /s/ Thian Hoo Tan
|      |  |               |  |                                       |  |                  
|      |  |               |  | Thian Hoo Tan
Chief Executive Officer