Abstract: Gallium oxide (Ga₂O₃), as a novel ultra-wide bandgap semiconductor material, possesses a bandgap of up to 4.8 eV and a critical breakdown field strength of 8 MV/cm, making it highly satisfy the requirements of power devices. However, the lack of p-type doping technology in Ga₂O₃ poses significant challenges to the realization of Ga₂O₃ homojunction devices. To address this problem, this study proposes a Junction Barrier Schottky (JBS) diode based on a p-NiO/n-Ga₂O₃ heterojunction, combined with field plates (FP) and mesa terminations, to enhance the DC performance of this device. TCAD simulation software was employed to provide theoretical guidance for the device design and fabrication. The results indicate that compared to a basic Schottky barrier diode (SBD), the breakdown voltage of the SBD with composite terminations increases from 887 V to 3069 V, with a slight increase in the forward conduction resistance from 3.975 mΩ·cm² to 5.395 mΩ·cm². Furthermore, the influence of p-NiO doping concentration and thickness on device performance was investigated. The present work demonstrats that the composite terminal structure effectively improves the reverse breakdown characteristics and provides theoretical insights for optimizing device performance.