epitaxial layers on silicon enables the use of existing silicon manufacturing infrastructure, eliminating the need for costly specific production facilities and leveraging large diameter silicon wafers at low cost. [10,11] Although silicon is a relatively cheap substrate compared with other substrate candidates, but has some distinct disadvantages since silicon and GaN are unmatched material systems. [12] The discrepancies in crystalline structure of GaN and silicon leads to higher lattice mismatches, behaving like dislocations and other types of defects. [13][14][15][16] The crystal defects affect the device performance and reliability to a large extent. A typical conundrum in GaN filed is related to the fact that the dislocations/lattice mismatch could exert inevitable negative effects on the device's basic performance, stability, and reliability. [17][18][19][20] Intensive researches indicated that charge trapping process caused by defects significantly affect the device performance. [21][22][23][24][25][26][27] As the most promising power device, gallium nitride (GaN)-based high electron mobility transistors (HEMTs) typically works under high voltage over a prolonged period. The long-term accumulation of heat during the operation appears to be another unfavorable factor that deteriorates the reliability. [28][29][30][31] The general degradation of electrical performance under negative bias condition at elevated temperatures is collectively known as negative bias temperature instability (NBTI) problem. [32] Although the NBTI problem was first noticed and mainly discussed in p-MOSFET devices, [33][34][35][36] it also perplexes depletion-mode or normally-ON GaN-HEMTs which is the most frequently used GaN device. [37][38][39][40][41][42][43][44] NBTI-related issues in depletion-mode GaN-HEMTs with different kinds of dielectric layer have been investigated in a series of researches. [41,[45][46][47][48][49][50] The NBTI-induced reliability issues in GaN-HEMTs have been acknowledged as a major concern that contributes to the operational instability. While intensive efforts have been made to optimize it from the perspective of manufacturing process or selected materials, [45,51,52] insufficient attention has been devoted to fundamental understanding of the intrinsic mechanisms. Some studies [41][42][43][44][45][46] attributed the degradation to the charge and discharge process of defects at the interface of GaN buffer layer and dielectric layer, while others [47][48][49][50] considered the degradation cause is not only the interface