August 15, 2019

Scott D. Beamer
Vice President and Chief Financial Officer
Cabot Microelectronics Corporation
870 North Commons Drive
Aurora, Illinois 60504

       Re: Cabot Microelectronics Corporation
           Form 10-K for the Fiscal Year Ended September 30, 2018
           Filed November 13, 2018
           Form 10-Q for the Quarterly Period Ended June 30, 2019
           Filed August 9, 2019
           File No. 000-30205

Dear Mr. Beamer:

       We have reviewed your filing and have the following comment. In some of
our
comments, we may ask you to provide us with information so we may better
understand your
disclosure.

       Please respond to this comment within ten business days by providing the
requested
information or advise us as soon as possible when you will respond. If you do
not believe our
comment applies to your facts and circumstances, please tell us why in your
response.

       After reviewing your response to this comment, we may have additional
comments.

Form 10-Q for the Quarterly Period Ended June 30, 2019

Reconciliation of Pro Forma and Non-GAAP Adjusted Pro Forma Information, page
49

1.    We note that you present full non-GAAP income statements on pages 50-53,
a
      presentation that appears to give more prominence to the non-GAAP
measures and is
      inconsistent with Question 102.10 of the Non-GAAP Financial Measures
Compliance and
      Disclosure Interpretations. Please review this guidance when preparing
your next filing.
      This should also be considered in your earnings releases furnished
pursuant to Item 2.02
      of Form 8-K.
        We remind you that the company and its management are responsible for
the accuracy
and adequacy of their disclosures, notwithstanding any review, comments, action
or absence of
action by the staff.
 Scott D. Beamer
Cabot Microelectronics Corporation
August 15, 2019
Page 2



      You may contact Michael Fay, Staff Accountant, at (202) 551-3812 or Brian
Cascio,
Accounting Branch Chief, at (202) 551-3676 with any questions.



FirstName LastNameScott D. Beamer                       Sincerely,
Comapany NameCabot Microelectronics Corporation
                                                        Division of Corporation
Finance
August 15, 2019 Page 2                                  Office of Electronics
and Machinery
FirstName LastName