Abstract: Gallium oxide (β-Ga₂O₃), an ultra-wide bandgap semiconductor with a bandgap of approximately 4.9 eV, exhibits a high critical breakdown electric field of 8 MV·cm⁻¹ and an excellent Baliga's figure of merit. These properties render it highly advantageous for next-generation high-voltage and low-power consumption power electronics. However, its device performance is limited by challenges in achieving p-type doping. Hexagonal boron nitride (h-BN), a high-performance ultra-wide bandgap semiconductor material with a bandgap of approximately 6.0 eV, not only demonstrates an exceptionally high breakdown electric field and thermal conductivity but also facilitates more stable p-type doping compared to β-Ga₂O₃. This characteristic presents an ideal material solution to address the p-type doping challenges inherent in traditional β-Ga₂O₃ devices. In this study, an innovative h-BN/β-Ga₂O₃ heterojunction diode is proposed to overcome the low V_B limitation of conventional Ga₂O₃ diodes. Furthermore, a composite termination structure incorporating trenches and field-limiting rings is designed through TCAD simulation to enhance the device's breakdown voltage. Compared to a basic Ga₂O₃ Schottky diode with a V_B of 416 V, the proposed h-BN/β-Ga₂O₃ heterojunction diode achieves a V_B of 524 V, representing a 25.7% improvement in voltage resistance. After optimizing the device termination structure, the final breakdown voltage increases to 2480 V, achieving a performance enhancement of 473.28%. This work effectively addresses the challenges of p-type doping in Ga₂O₃ and electric field concentration through the design of the h-BN/β-Ga₂O₃ heterojunction and high-voltage termination structure, offering a significant technical reference for the advancement of high-voltage Ga₂O₃ diodes.