We fabricated highly sensitive room temperature hydrogen sensors based on SnO2 films. The films were deposited by the photochemical deposition. The deposition solution containing 10 mmol/L of SnSO4 was dropped on the substrate and irradiated with light of an Hg arc lamp. The sample annealed at 200 degrees C showed resistance decrease by a factor >10(3) for a 0.05% H-2 + Ar mixed gas (0.1 atm) at room temperature. The sensitivity and response speed were further improved by UV irradiation using a low-pressure Hg lamp both in vacuum and in air. (c) 2011 Elsevier Ltd. All rights reserved.