Doping the III-nitrides p-type by ion implantation is a challenge due to the implantation-induced damage and associated compensation. In this chapter, we focus on ultra-high pressure annealing (UHPA)-based activation and damage recovery to achieve p-type selective area doping in GaN. The UHP annealing is conducted at temperatures from 1300 to 1480 °C under nitrogen pressures of 0.3–1 GPa to stabilize the surface of the GaN. Crystalline damage recovery and Mg activation are found to be a function of annealing temperature and time. A “diffusion budget” related to the dopant diffusion length is employed to compare samples annealed at different temperatures and for different times. Although damage recovery, as measured by XRD, was achieved at relatively low diffusion budgets, no p-type conductivity was observed due to compensation by implantation-induced defects. Higher diffusion budgets were required to achieve a low Mg ionization energy <150 meV and Mg activation >70%. Ion co-implantation was used to diminish point defects and the associated leakage currents, boosting the p-type doping efficiency in GaN while limiting diffusion. A kV-class junction barrier Schottky diode (JBS) with a near-unity ideality factor and low differential RON of 0.6 mΩ·cm2 was demonstrated via selective area p-type doping in GaN.