A thermoelectric hydrogen gas sensor developed for leak detection in hydrogen stations has shown good hydrogen selectivity and wide hydrogen detection concentration ranging from 0.5 ppm to 5 %. We have demonstrated high sensitivity and reliability of the sensor exceeding conventional technology through a field test of one year. We could optimize the following three constituent technology elements to meet the social needs, i.e. new principle integrating catalytic combustion and thermoelectric conversion technology, micro-fabrication technology to realize the principle and high performance ceramic catalyst for gas combustion. In addition, the sensor performance evaluation technology established during the development has been proposed for ISO standardization.