Monitoring hydrogen levels in radioactive environments is important in nuclear energy safety and space study because leakage of this gas can cause destructive detonation. Herein, hydrogen gas sensing devices were fabricated by using a simple design of a planartype structure sensor containing a SnO2 thin film sensitized with microsized Pd islands. In addition, the effects of gamma irradiation on sensor performance were investigated and results revealed that low doses of gamma irradiation had ignorable effect on the sensing performance of the device. However, a relatively high dose of gamma irradiation improved the sensitivity of the device because of oxygen defect generation. The enhancement of hydrogen gas-sensing characteristics was correlated with microstructure and optical characterization. Results show that gamma irradiation induced defects in the SnO2 thin film, controlling the doping level, and thus enhancing the gas-sensing characteristic of the device. The sensor can be used for monitoring hydrogen gas at low concentrations of 50 ppm-500 ppm, with fast response and recovery time, making it suitable for potential safety applications in monitoring hydrogen levels in radioactive environments. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.