Large-scale synthesis of GaN nanowires was grown on c-sapphire substrate by chemical vapor deposition technique. X-ray diffraction, field emission scanning electron microscopy, mu-Raman and mu-photoluminescence analyses reveal that GaN nanowires crystallize within a hexagonal wurtzite-type structure with a considerably high yield, high aspect ratio of GaN NWs having an average diameter and length of 80 nm and up to several microns, respectively. A metal semiconductor metal (MSM) gas sensor using GaN nanowires was fabricated and hydrogen (H-2)-sensing performances were examined over broad range of concentrations (7-1000 ppm) and at various operating temperatures (25,100, 150 degrees C). The NWs demonstrated high sensitivity up to 255% upon exposure to 1000 ppm of H-2 gas at room temperature at a low power consumption of 60 mu W. Additionally, at room temperature, the sensor exhibited a significant sensitivity of 83% when exposed to a very low H-2 gas concentration of 34 ppm then becomes 15% at ultra low level of 7 ppm. The sensing measurements of NWs based sensor for H-2 gas in the temperatures range of 25-150 degrees C were repeatable and reversible over a period of time of 50 mm. The sensor exhibited free hysteresis phenomena after exposed to various H-2 concentrations at various temperatures. The high performance of the fabricated sensor was attributed mainly to the large surface-to-volume ratio as well as the high crystallinity of the synthesized GaN NWs. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.