In this paper, we present a new top-down fabrication method of silicon nanowires (SiNWs) for inertial sensor applications. Recently, SiNW piezoresistive inertial sensors have attracted much attention because they can provide high sensitivities and high signal-to-noise ratios. For manufacturable inertial sensors based on SiNWs, the dimensions of SiNWs need to be reproducible and controllable. SiNWs should also be integrated with microscale structures and circuits. In the developed method, the width and thickness of SiNWs were controlled by thermal oxidation and silicon wet etching, respectively. SiNWs can be integrated with microscale structures, which were also fabricated by deep reactive ion etching and silicon wet etching. The width and thickness of the fabricated SiNWs were in the range of 65–163 and 56–131 nm, respectively. The reproducibility of SiNWs was also evaluated. The maximum standard deviation of the width of SiNWs was 30 nm, and that of the thickness was 46 nm. These results show that the SiNW dimensions are reproducible and that they can be accurately controlled.