Gallium nitride (GaN) single crystal with prominent electron mobility and heat resistance have great potential in the high temperature integrate electric power systems. However, the sluggish charge storage kinetics and inadequate energy densities are bottlenecks to its practical application. Herein, the self-supported GaN/Mn₃O₄ integrated electrode is developed for both energy harvesting and storage under the high temperature environment. The experimental and theoretical calculations results reveal that such integrated structures with Mn-N heterointerface bring abundant active sites and reconstruct low-energy barrier channels for efficient charge transferring, reasonably optimizing the ions adsorption ability and strengthening the structural stability. Consequently, the assembled GaN based supercapacitors deliver the power density of 34.0 mW cm⁻² with capacitance retention of 81.3% after 10000 cycles at 130 ℃. This work innovatively correlates the centimeter scale GaN single crystal with ideal theoretical capacity Mn₃O₄ and provides an effective avenue for the follow-up energy storage applications of the wide bandgap semiconductor.