In this paper we report on the characteristics of Pd/GaN and Pd/Si Schottky barriers exposed to different gases at various temperature range from 25 degrees C to 500 degrees C. The characteristics of Pd/GaN and Pd/Si Schottky barriers as gas sensors were measured as a function of temperature and ambient. Both types of sensor show changes in forward current upon introduction of different gases (N-2, air, H-2) into the ambient. The devices can be operated at large forward current, leading to large signal size for current at short response time for switching from one gas ambient to another such as N-2 to H-2 (2%) in N-2. The signal size increases with the increase in measurement temperature due to more efficient cracking of the gas molecules. Both types of devices appear well suited to combustion control and leak detection.