We report a study of the ultraviolet (UV) irradiation effects on the wet chemical etching of unintentionally dopedn-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated with a 253.7 nm mercury line source, etching of GaN is found to take place in aqueous phosphorus acid(H3PO4)and potassium hydroxide (KOH) solutions ofpHvalues ranging from−1to 2 and 11 to 15, respectively. Formation of gallium oxide is observed on GaN when illuminated in diluteH3PO4and KOH solutions. These results are attributed to a two-step reaction process upon which the UV irradiation is shown to enhance the oxidative dissolution of GaN. ©1998 American Institute of Physics.