For safety reasons, while handling fuel cells, hydrogen concentrations of 0.1 -3% and above need to be detected. Low power hydrogen sensors, based on a Field Effect Transistor (FET), have been in use for about 25 years. In the past platinum and palladium were often used as gas sensitive layers. Unfortunately in the required concentration range, the Pt based sensors have a poor selectivity at room temperature and were not stable at operating temperatures above 60degC. To solve this problem Pt with a porous tin oxide (SnO 2 ) top layer is used as a chemically sensitive electrode in a Floating Gate Field Effect Transistor (FG -FET). The results show that the SnO 2 film on Pt stabilizes the sensor signal response between room temperature and 135degC. Also the sensor response time with t 50 < 10s is quite fast and the cross sensitivity to other gases compared to pure Pt is reduced.