In this paper, a fabrication process which utilizes both photoresist(PR) and silicon oxide layer as etch mask for deep reactive-ion etching(DRIE) is presented for forming high-aspect-ratio silicon structures without severe residual stress. An oxide layer was deposited and patterned only critical parts as a pick-off in inertial sensors, then a PR layer was deposited and patterned other parts which are relatively less sensitive to the precision of a pattern. After DRIE process, both etch masks have been removed. The fabricated device using this 2-step mask shows reduced residual stress and more precise structures compared with the device using a conventional single silicon oxide and PR mask, respectively.