Chemical mechanical polishing of gallium nitride with collodial silica has been demonstrated. Removal rates and ultimate surface roughnesses have been found to depend on sample polarity (either A or B faced) as well as the pH of the polishing fluid and the initial surface morphology. High quality A-faced samples exhibited no polishing action while B-faced material was readily removed. Removal rates at room temperature were found to vary from 0.4 to 1.1 mum/h resulting in surface roughnesses as low as 1.1 nm root mean square roughness (RMS) over 400 mum(2) decreasing to 0.4 nm RMS over 25 mum(2). Investigations into the mechanism of polishing reveal both a chemical and mechanical aspect to polishing GaN with colloidal silica. (C) 2002 The Electrochemical Society.