For GaN digital circuits, the p-GaN high electron mobility transistor (HEMT) is widely adopted as an enhancement-mode device. To convert enhancement-mode devices into depletion-mode ones, traditional methods of achieving depletion-mode operation rely on high-energy ion etching to selectively remove portions of the p-GaN layer. However, this etching process often leads to surface lattice damage andincrease in interface state density, resulting in the formation of gate-edge leakage paths. These issues lead dynamic on-resistance to increase and long-term reliability to decrease. Instead, hydrogen ion implantation has been used as a non-destructive doping modulation technique to mitigate these challenges. In view of this, in this study hydrogen ion implanted technology is adopted to achieve the transition of enhancement-mode p-GaN HEMTs to depletion-mode HEMTs. By employing temperature-dependent current-voltage (T-I-V) sweeping, low-frequency noise analysis, and lock-in infrared imaging techniques, the forward current transport, degradation and breakdown behaviors are investigated. The results are shown below. 1) The gate forward T-I-V curves exhibit a significant power-law relationship in double logarithmic coordinates, the current slope is insensitive to temperature, and the activation energy is derived to be ~52 meV. Neither of the classic pn junction theory and the space charge limited current model can explain the current behavior, whereas a defect-mediated electron hopping mechanism is identified as the dominant transport mechanism. 2) A long term of gate bias stress leads to the degradation into a typical rectifying behavior, indicating that the p-GaN region undergoes reconstruction in certain areas. The forward current exhibits an ideality factor of approximately 2.6 and a typical 1/f noise spectrum, indicating that the defect-assisted tunneling current is dominant. 3) High gate bias induces a current breakdown. Lock-in infrared imaging and pixel-by-pixel correction techniques are used to respectively obtain the breakdown site and the “hot spots” temperature.