In this work, GaN nanowires have been formed on Si substrate using production standard stepper lithography and top-down approach. Three different functionalized devices were prepared by the deposition of metal oxides- ZnO, WO3 and SnO2 by optimized RF sputtering on nanowires followed by rapid thermal annealing. The elemental composition, crystallinity and surface topography of metal-oxide/GaN nanowires were fully characterized by EDS, XRD, AFM and SEM. The SO2 gas sensing data was collected and analyzed for all three sensors. The ZnO/GaN sensor was found to be the best candidate for precise SO2 detection. To examine the real-world applicability of ZnO/GaN sensor device, its additional sensing properties, including gas sensing adsorption and desorption rate, cross-sensitivity to interfering gases, and long-term stability at various environmental conditions were investigated. Furthermore, principal component analysis has been performed to address the cross-sensitive behavior of ZnO. The SO2 sensing mechanism on metal-oxide/GaN under UV irradiation was discussed as well. Results demonstrate that ZnO functionalized GaN nanowire can be employed as a high performance SO2 sensor.