The dependence of the etch rate and etch morphology on photoelectrochemical (PEC) process conditions is reported. Considerable control over the etch rate and surface roughness can be exerted through selection of the electrolyte concentration, illumination intensity, as well as-through the use of bias voltage applied during the PEC etch process. The etch rate for n-type GaN was dramatically enhanced from 10 to 32 nm/min by the application of +2 V bias during PEC etching. In addition, the surface morphology can be controlled by applying a bias voltage; smooth etched surfaces with root-mean-square (rms) roughness of 0.5 nm have been obtained with bias of +0.65 V, comparable to as-grown surfaces, compared to a rms roughness of 8 nm when no bias is applied. The use of reverse bias voltages was found to suppress PEC etching and produce rough surfaces. The etch rate and morphology have been found to depend on the n-type GaN doping density, with highly doped material resulting in slower etch rates and rougher surfaces than for lightly doped material under the same etch conditions. (C) 2004 American Vacuum Society.