A novel activation process for Mg-implanted GaN was demonstrated. As opposed to the conventional thermal annealing process, an H 2 /NH 3 alternating supply annealing process achieved better optical activation, stronger near-ultraviolet luminescence and weaker yellow luminescence in the photoluminescence spectroscopy. After this process, small hexagonal hillocks were observed on the surface, which indicated that crystal regrowth was induced by this process, consisting of decomposition of GaN by H 2 supplies and re-crystallization by NH 3 supplies. It was revealed that the implanted Mg could easily be located at the activation site by means of crystal regrowth by this process.