We characterized the surface defects in a-plane GaN, grown onto r-plane sapphire using a defect-selective etching (DSE) method. The surface morphology of etching pits in a-plane GaN was investigated by using different combination ratios of H3PO4 and H2SO4 etching media. Different local etching rates between smooth and defect-related surfaces caused variation of the etch pits made by a 1: 3 ratio of H3PO4/H2SO4 etching solution. Analysis results of surface morphology and composition after etching by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrated that wet chemical etching conditions could show the differences in surface morphology and chemical bonding on the a-plane GaN surface. The etch pits density (EPD) was determined as 3.1x10(8) cm(-2) by atom force microscopy (AFM). (C) Published by Elsevier B.V.