The method of defect-selective etching of Ga polar (0 0 0 1) surface of GaN single crystals and epitaxial layers is presented. Etching is performed in molten KOH-NaOH eutectic (E) with an addition of 10wt% of MgO powder (E + M). At temperatures above the melting point of E, a sticky droplet of etch is formed, which allows revealing of defects on one side of the crystal only, leaving the other side intact. This method is advantageous for defect study on Ga-polar surface of GaN single crystals, because the much higher temperature required for etching of this surface will not result in the fast dissolution of N-polar side. The reliability of the method has been confirmed by: (i) revealing of the indentation-induced dislocations in the GaN single crystals and (ii) comparison of the results of (E + M) etching with photoelectrochemical etching and transmission electron microscopy on hetero-epitaxial layers. (C) 2002 Elsevier Science B.V. All rights reserved.