The selective etch characteristics of GaN, AlxGa1-xN, and InxGa1-xN have been examined in an inductively coupled plasma reactor using Cl-2/Ar/O-2 as the etchant gas. Etch rates and selectivities were strongly influenced by the flow rate of oxygen as well as the plasma parameters. Etch rates as high as 5500 Angstrom/min were obtained for GaN, 1850 Angstrom/min for Al0.05Ga0.95N, 420 Angstrom/min for Al0.1Ca0.9N, and 2589 Angstrom/min for In0.12Ga0.88N. Moreover, the etch selectivities of GaN and the In0.12Ga0.88N over the Al0.1Ga0.9N were as high as 24 and 32, respectively. These are the highest values ever reported for an AlGaN film with a relatively low Al composition (x = 0.1). An x-ray photoelectron spectroscopy analysis of the etched surface showed that an Al-O bond was formed on the AlGaN surface during the Cl-2/Ar/O-2 plasma etching and the high selectivity thus obtained could be attributed to the etch-resistant aluminum oxide layer. This oxide layer could be easily etched off by a HE-based solution during the mask removal process.