Pt/SiO2/GaN (MIS) and Pt/GaN (MS) Schottky diodes exhibit hydrogen-sensing characteristics, including forward sensitivity ratios (S-F) of 14685 and 603.9, reverse sensitivity ratios (S-R) of 44636 and 5626 (in 9970 ppm H-2/air), and Schottky barrier height variations (Delta phi(b)) of 231.6 and 195.9 meV (in 9970 ppm H-2/air) at 300 K, respectively. As compared with the MS device, the studied MIS device manifests a larger hydrogen-detection capability. This result implies that the SiO2 insulator surface plays a strikingly important role in producing the excellent hydrogen-sensing response. Furthermore, reproducible responses at various temperatures are also realized. (C) 2007 The Electrochemical Society.