High Electron Mobility Transistors (HEMTs) are widely recognized for their exceptional performance in high-frequency applications, yet improvements are still needed in areas of low power consumption and high efficiency. To enhance overall performance, this paper proposes a novel structure, integrating a thin AlGaN cap layer between the p-GaN and the gate metal within a developed stepped hybrid buffer layer HEMT. Observations of the electric field distribution in TCAD simulations further confirmed the formation of a dual junction. The advantages of this structure include an increased overall device performance, featuring a threshold voltage of 2.3V, a gate current of only 4.810-7 A/mm, an output current of 0.25 A/mm, a BFOM value reaching 1.48 GW/cm2, and a breakdown voltage is 1454V. These characteristics hold potential for emerging applications such as 5G communications and electric vehicle power control systems. The results of this study not only help deepen the understanding of the impact of the AlGaN cap layer on HEMT performance but also provide new ideas and directions for the design and optimization of future.