GaN etching was performed using planar inductively coupled Cl-2/Ar plasmas, and the effects of main process parameters on the characteristics of the plasmas and their relations to GaN etch rates were studied. GaN etch rates increased with the increase of chlorine radical density and ion energy, and a vertical etch profile having an etch rate close to 400 nm/min could be obtained. The GaN etch rate appeared tu be more affected by the chemical reaction between Cl radicals and GaN compared to the physical sputtering itself. This GaN etch mechanism was studied using Langmuir probe and optical emission spectroscopy (OES) during etching, and X-ray photoelectron spectroscopy (XPS) of the etched surfaces.