Au/TiO2/GaN junctions with a TiO(2 )interlayer were deposited at various oxygen pressures from 5 mTorr to 80 mTorr, and their surface, microstructural, and electrical properties were investigated. Compared with a single 5 pm-Si-doped GaN film on an (0001) AlO3 substrate, the 0.2 pm-Si-doped GaN film with an undoped GaN buffer layer demonstrated improved properties for the application to metal/semiconductor junctions. Atomic force microscope and tunneling electron microscope measurements suggested that the TiO2 interlayer deposited at room temperature exhibited a distinctive change above the oxygen deposition pressure of 40 mTorr. In contrast to the small rectification ratio of 10(1)-10(2) for Au/GaN junctions, the Au/TiO2/GaN junctions with the TiO2 interlayers displayed a large rectification ratio of 10(6)-10(7) when the oxygen pressure during the deposition of TiO2 interlayer was maintained at 40 mTorr. These results suggest that the leakage current and the rectification behavior in a metal/oxide/semiconductor junction can be effectively controlled using the oxygen deposition pressure for an oxide interlayer.