Photoelectrochemical etching and oxidation of the sidewall structures of InGaN light-emitting diodes has been utilized to significantly improve optical emission efficiency. Only with an H2O solution can n-type InGaN/GaN multi-quantum-well (MQW) and n-type GaN:Si layers be selectively etched off from the p-type GaN:Mg epitaxial layer. In addition, the sidewall of n-type MQW/n-type GaN layers will be oxidized and etched simultaneously. This is attributed to the interposing of a Ga2O3 layer with a low reflective index between the GaN and air as well as with the rough Ga2O3/GaN structures. Under a 20 mA operating current, and after a 10 min photoelectrochemical (PEC) oxidation process, the light output power increased by 42%. This PEC oxidizing and etching process is suitable for high-power nitride-based light-emitting diode lighting applications. (c) 2005 The Electrochemical Society.