It is the first time that Zinc Oxide (ZnO) nanowires and Titanium Dioxide (TiO₂) nanowires structures are fabricated on the Silicon (Si) micropillars surface to form ZnO nanowires/TiO₂ nanowires/Si micropillars structure successfully. And this structure is applied to the gas sensor. The Si wafer with countless micropillars is used as substrates, which are fabricated by Cesium Chloride (CsCl) self-assembly lithography and dry etching. The TiO₂ nanowires and ZnO nanowires are prepared by hydrothermal reaction separately. From the SEM images, 60 minutes ZnO nanowires growth and 3 hours TiO₂ nanowires growth on 600 nm average diameter and 3.2 µm height Si micropillars is the most suitable morphology for the gas sensor application. From the XRD curves, both the ZnO and TiO₂ nanowires on the Si micropillars surface are good crystallinity. Compared with the ZnO nanowires/Si micropillars structure, the ZnO nanowires/TiO₂ nanowires/Si micropillars can increase the response to ethanol no matter the concentration. For 500 ppm ethanol, the response from ZnO nanowires/TiO₂ nanowires/Si micropillars is about 76%, which is much higher than the 44% of that from ZnO nanowires/Si micropillars.