Inductively coup led plasma ( ICP) etching of back－illuminated Al0. 45 Ga0. 55N grown bymetalorganic chemi－cal vapor deposition was investigated in Cl2 /Ar/He plasmas. Ion beam sputtering deposited Ni was used as etching mask. The measured etching rates increased with the increasing ICP dcbias. The changes ofAlGaN sheet resistance were measured by using transmission line model ( TLM). According to the TLM measurement results the electrical damage was analyzed as a function of dc bias. Scanning electron microscope was used to evaluate the etch profiles at different dc bias.