GaN Schottky barrier UV photodetectors (PDs) with a beta-Ga2O3 cap layer realized by furnace oxidation of GaN epitaxial layer were fabricated and characterized. With the cap layer inserted, it was found that the reverse leakage current could be reduced by more than 4 orders of magnitude and the UV-to-visible rejection ratio increased by 21 times. When compared with the conventional GaN PDs, incorporating an additional beta-Ga2O3 cap layer helps to reduce the noise level and at the same time achieve a larger detectivity. (C) 2012 The Japan Society of Applied Physics