The characteristics of Pt/GaN and Pt/4H-SiC Schottky diodes as gas sensors were measured as a function of temperature and ambient. Both types of diode rectifiers show rapid (< 1 s) changes in forward current upon introduction of different gases (N-2, air, H-2, CF4) into the ambient. The diodes can be operated at large forward currents, leading to large signal sizes for switching from one gas ambient to another. For GaN, a shift of similar to0.2 V at 25degreesC and similar to0.7 V at 150degreesC was obtained at a fixed forward current for switching from N-2 to 10% Hz in N-2. For SiC, under similar conditions, shift of 1.34 V at 25degreesC was obtained at a fixed forward current of 0.2 A for switching from N-2 to 10% H-2 in N-2. The signal size increases with increasing measurement temperature due to more efficient cracking of the gas molecules. Both types of devices appear well suited to combustion control and leak detection. (C) 2003 Elsevier Science Ltd. All rights reserved.