A Study of the electrochemistry of n-type GaN in an alkaline peroxydisulfate S2O82- solution was used to explain the mechanism of photoetching of the semiconductor under open-circuit conditions. The observed enhancement of the photoetch rate as a result of platinum either directly on or in electrical contact with the semiconductor is shown to be mainly a photogalvanic effect. The factors determining the etching kinetics and surface morphology are elucidated. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3183807] All rights reserved.