Schottky diodes on AlGaN/GaN heterostructures with Pt, IrPt, and PdAg catalytic metals are fabricated and characterized from 200 degrees C to 800 degrees C for H-2 sensing. Over this large range of temperature, the forward current of all the diodes increases with exposure to H-2 gas, which is attributed to Schottky barrier height reduction caused by the atomic hydrogen absorption on the metal-oxide interface. The results indicate that AlGaN/GaN heterostructure Schottky diodes are capable of high-temperature H-2 sensor operation up to 800 degrees C. As temperature increases, the hydrogen detection sensitivity of Pt and IrPt diodes improves due to the more effective H-2 dissociation. However, the sensitivity of PdAg diodes degrades with the increase of temperature due to thermal instability of PdAg. At a range of temperature from 200 degrees C to 300 degrees C, PdAg diodes exhibit significant higher sensitivity compared with Pt and IrPt diodes. IrPt and Pt diodes show higher sensitivity at temperatures above 400 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.