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This paper describes an improvement of Si/SiO/sub 2/ mask etching selectivity in the new D-RIE process that we presented in MEMS 2000. This process, which repeats the conventional D-RIE (ASE process) and O/sub 2/ plasma irradiation processes alternately, can improve the aspect ratio due to the prevention of lateral etching. However, the SiO/sub 2/ mask erosion of this process was 2.7 times as high as that of the conventional D-RIE process because the SiO/sub 2/ mask is sputtered by oxygen ion in the O/sub 2/ plasma irradiation process. Therefore the highest aspect ratio:46 was restricted by mask consumption. In this study, we suppressed the SiO/sub 2/ mask consumption. This suppression improves etching selectivity and increases the highest aspect ratio up to 60. Furthermore, the required process time is reduced to 2/3 of the prior result.