Single-crystal gallium nitride (GaN) has been expected to be applicable for power devices with low power loss. However, GaN materials show high hardness, high chemical stability, and brittleness, and are therefore difficult to process with conventional silicon substrate methods. This study was performed to improve the processing efficiency by oxidizing the Ga surface of GaN material using hydroxyl (OH) radicals generated by ultraviolet (UV) irradiation of hydrogen peroxide (HP) solution. Furthermore, we developed a UV-assisted tape grinding method that can perform oxidization and removal continuously. The results indicated that the developed processing method improved the processing speed by more than sixfold compared to the standard processing method.