<p>With the advancement of the global energy transition, power electronic systems are upgrading towards high efficiency and high reliability. Traditional power electronic devices, due to inherent defects such as narrow bandgap and poor high-temperature stability, have made it difficult to meet the performance requirements of advanced applications. At present, field-effect transistors based on gallium nitride still face key problems, including current collapse, insufficient gate reliability, poor coordination between material and structural design, and limited adaptability to complex environments. Thus, a power electronic device based on aluminum gallium nitride/gallium nitride heterojunctions was proposed. By designing a composite structure consisting of a source field plate, gate silicon nitride passivation, and back barrier injection, and optimizing the growth and packaging processes of metal-organic chemical vapor deposition heterojunctions, the device efficiency and reliability were improved. Experimental results show that this device performs exceptionally well in multidimensional tests, including wet-heat aging, mechanical vibration, and electrical stress cycling. In the electrical stress cycling test, the forward conduction resistance of the component changed by 0.03 ± 0.005 Ω, and the reverse recovery time changed by 5 ± 1 ns. In the surge current test, the component was not damaged, and the parameters fluctuated normally. This paper provides a practical and feasible technical solution for the engineering application of wide-bandgap semiconductor materials in complex power electronics scenarios.</p>