©2019 The Ceramic Society of Japan. All rights reserved. Thermoelectric gas sensors (TGSs) were developed using a series of materials combined with gas-selective combustion catalysts. The TGSs have a micro-device structure formed on a membrane-type micro-hotplate to enhance their sensitivity. The working principle of the TGSs involves a synergetic combination of thermoelectric detection and the catalytic combustion of detection gas, which can eliminate the effects of humidity and other inflammable gases, allowing highly sensitive gas detection. This paper introduces the thin-film processing and the methodology of integrating the ceramic catalyst on the micro-device for the TGSs, and the mass production of gas sensors was demonstrated in this study. The TGSs can detect a wide H concentration range of several parts per million (ppm) to percent in air, exhibiting robust sensing performance with long-term stability. We developed new applications such as breath H 2 measurement with a H 2 concentration of 0200 ppm.