A low- Magnesium (Mg) out-diffusion normally off p-GaN gated AlGaN/GaN high-electron-mobility transistor (HEMT) was developed using a low-temperature laser activation technique. Conventionally, during the actual p-GaN layer activation procedure, Mg out-diffuses into the AlGaN barrier and GaN channel at high temperatures. In addition, the Al of the AlGaN barrier layer is injected into GaN to generate alloy scattering and to suppress current density. In this study, the GaN doped Mg layer (Mg:GaN)was activated using short-wavelength Nd:YAG pulse laser annealing, and a conventional thermal activation device was processed for comparison. The results demonstrated that the laser activation technique in p-GaN HEMT suppressed the Mg out-diffusion-induced leakage current and trapping effect and enhanced the current density and breakdown voltage. Therefore, using this novel technique, a high and active Mg concentration and a favorable doping confinement can be obtained in the p-GaN layer to realize a stable enhancement-mode operation.