Hydrogen sensing characteristics of a novel metal-oxide-semiconductor (MOS) Schottky diode are thoroughly investigated. The MOS structure consists of a gallium nitride (GaN)-based semiconductor system, a nickel oxide (NiO) layer, and palladium (Pd) catalytic materials. A well-prepared Pd/NiO/GaN-based diode shows several advantages in relation to hydrogen sensing, including a simple structure, high sensing speed, wide flexibility for operation under both forward and reverse applied voltages, and a good sensing response of 8.1 x 10(3) under an applied forward voltage of 0.25 V, at 300 K in a 1% H-2/air ambience. Furthermore, under an applied reverse voltage of -2 V and at a high temperature of 573 K, this MOS diode shows a response as high as 1.8 x 10(4) towards 1% H-2/air mixture gas. The Schottky diode sensor with a novel Pd/NiO/GaN structure demonstrated in this study is a promising candidate for high-performance hydrogen sensing applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.