The roughness of GaN surfaces produced by photoenhanced electrochemical etching is significantly reduced by the introduction of an external bias voltage during the etching process. The root-mean-square surface roughness decreases from a maximum of approximately 1700 nm to a minimum of 20 nm as the bias voltage is increased from 0 to 2.5 V, and as the KOH concentration is decreased from 1.0 to 0.01 M. Etch rates as high as 0.4 mu m/min are achieved at room temperature, producing surfaces with roughnesses of only 20 nm.