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A reliable and high-performance oxygen (O 2) sensor based on TiO 2 -decorated bridging Gallium Nitride nanowires (TiO 2 /GaN NWs) was fabricated, which operates under ultraviolet (UV) irradiation at room temperature (RT). The TiO 2 /GaN NWs were prepared by direct-bridge growth of GaN NWs across the trench of GaN coated sapphire substrate, followed by titanium (Ti) sputtering and thermal oxidation. The morphology characteristic shows that TiO 2 nanoparticles (NPs) are anchored uniformly on the surface of GaN NWs. The sensors with various TiO 2 film thickness (0, 2, 5, 10 nm) were measured at RT under 365 nm UV illumination with O 2 concentrations varying from 1% to 25%. Experimental results show that when the TiO 2 film thickness is 5 nm, the O 2 response reaches its maximum and the limit of detection (LOD) as low as 0.45% O 2. Moreover, the 5 nm TiO 2 /GaN NWs sensor were also measured under different wavelengths (λ = 280, 365, 450 nm) UV illumination and found that the lower light wavelength, the higher O 2 sensing. In addition, the sensor has excellent repeatability, selectivity and long-term stability, thus has a wide application in the field of O 2 gas sensing. [Display omitted] • A oxygen gas sensor based on TiO 2 /GaN NWs was fabricated and well studied. • The sensor operates in air atmosphere under UV illumination (λ = 365 nm) at room temperature (∼25 ℃). • When the TiO 2 thickness is 5 nm, the O 2 response reaches its maximum and the limit of detection ∼ 0.45% O 2. • The sensor has excellent repeatability, selectivity and long-term stability. • Oxygen response under different UV wavelengths was also studied. [ABSTRACT FROM AUTHOR]