An alternative method for achieving etching selectivity between GaN and AIN has been demonstrated. The etch rate of AW was significantly decreased by the addition of a low concentration of O-2 to a Cl-2-Ar mixture in an inductively coupled plasma (ICP) etching system. The etch rate of GaN in the O-2-containing plasma was approximately 15% less than the plasma without the O-2 for the same parameters. The pressure and the ICP power were varied to achieve a maximum selectivity of 48 at a pressure of 10 mTorr, a direct current bias of - 150 V, and an ICP power of 500 W. The etch rates of GaN and ALN at these parameters were 4800 and 100 Angstrom/min, respectively.