The highly oriented diamond films are deposited on the mirror-polished Si(001) substrate by the cyclic hydrogen etching treatment during bias enhanced nucleation (BEN) process using a microwave plasma deposition system. The number of oriented diamond grains treated by the hydrogen etching during the BEN process are about two-times higher than that treated by normal BEN processes. The (111) X-ray pole figure of the oriented diamond film is clearly dominated by the four (100) peaks of diamond. The full width at half maximum of X-ray (111) poles and X-ray (004) peak rocking curves of diamond deposited by the cyclic hydrogen etching treatment during the BEN process is smaller than that by normal BEN treatment. From the results and our previously suggested model, we discuss the roles of hydrogen to nucleate the oriented diamond on Si by the BEN process. (C) 1999 Published by Elsevier Science S.A. All rights reserved.