AbstractInGaN/GaN multi‐quantum‐well light‐emitting diodes (MQW LEDs) are grown through a metal‐organic chemical vapor deposition (MOCVD) System. The fabricated GaN‐based LED wafers are treated with a photoelectrochemical (PEC) wet etching process using a Hg lamp illumination and KOH solution. The band‐gap selected wet etching process of InGaN/GaN MQW layer was observed from the mesa sidewall between the p‐type and n‐type GaN interface which has the 4.2 (m/hr lateral etching rate. The emission wavelength of the etching treated LED and standard LED were located at 458 nm. The light output power of the PEC etching LED had 2.04, 5.94, and 1.73 times enhancement measured from the from‐side, lateral‐direction, and back‐side compared with the standard ones. The light output power have stronger enhancement caused by forming the triangle‐shaped air holes located at the active layer region, grain‐like roughening surface and nano‐scale triangle pits on the mesa sidewall. The light scattering by this roughening sidewall was increased to enhance the light extraction efficiency. This PEC sidewall etching process is suitable for high power Nitride‐based LEDs lighting applications. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)