A room-temperature photoelectrochemical etching process forn-type GaN films using a 0.04 M KOH solution and Hg arc lamp illumination is described. The process provides highly anisotropic etch profiles and high etch rates (>300 nm/min) at moderate light intensities (50mW/cm2&at;365 nm). The etch rate and photocurrent are characterized as a function of light intensity for stirred and unstirred solutions, and the etch process is found to be diffusion limited for light intensities greater than 20mW/cm2&at;365 nm. A reaction mechanism for the etch process is proposed. ©1997 American Institute of Physics.