This work investigates the morphology of GaN etched in hydrogen (H 2) at different temperatures, the activation energies of the rate-limiting steps of H 2 etching, and the overgrowth on a H 2-etched GaN template. The surfaces of GaN have different profiles after being etched in H 2; they resemble a plane decorated with columns and mooring posts in a low-temperature etching condition, and with deep cavities in a high-temperature etching condition. The etched profiles show that H 2 etching has controllable etching directions: vertical and lateral. In a low-temperature condition, H 2 etching has both vertical and lateral etching directions; however, in a high-temperature condition, it has only the vertical etching direction. The activation energies of the rate-limiting steps under etching pressures of 100 and 700 Torr are estimated to be 3.22 and 3.77 eV, respectively. A thick GaN layer has been grown on a H 2-etched GaN template, and it has self-separated from the underlying sapphire substrate.