© 2018 WO3-based semiconductor-type gas sensors were fabricated, and their sensing properties to methylmercaptan (CH3SH) were examined in this study. The Ru loading on WO3was an effective way of an increase in the CH3SH response. In addition, the CH3SH response increased with a decrease in the operating temperature as well as with an increase in the thickness of the Ru-loaded WO3sensing layer. The increase in the porosity of the Ru-loaded WO3sensors, which were fabricated by utilizing polymethylmethacrylate microspheres as a template, was also effective in improving the CH3SH response, especially at a low temperature of 150 °C. In addition, the lamination of the Ru-loaded WO3sensor with an α-Al2O3film improved the CH3SH response at 200 °C. Moreover, the Ru loading on the WO3powder increased the catalytic activities of CH3SH oxidation, and CH3SH was partially oxidized to CH3SSCH3at temperatures less than 330 °C. It was suggested that the increase in the positively charged adsorption of the partially oxidized products onto the bottom part of the sensing layer is effective for enhancing the CH3SH response, especially at lower operating temperatures.