In this study, a Ni/GaN Schottky barrier diode (SBD) with both groove beveled and oxygen plasma terminations was fabricated and evaluated. The mixed termination structure was formed by inductive coupled plasma (ICP) in oxygen atmosphere. Confirmed by the measurement results of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), a 3.5-nm-thick GaOx passivation layer and beveled termination with an angle of 65° were identified around the edge of the electrode. Compared with the conventional samples, the treatment samples demonstrated the reverse leakage current reduced by one order of magnitude, the ON-resistance reduced by approximately 20%, and the breakdown voltage increased by 80%. Further technology computer-aided design (TCAD) simulation shows that the mixed termination structure can effectively inhibit the electric field concentration effect. Finally, temperature dependence characteristics show that the zero-temperature coefficient (ZTC) bias points of treatment samples locate in the low-voltage region, indicating that the devices are more suitable for the integrated circuit (IC).