Cathodoluminescence (CL) mapping and selective-etching techniques were used to characterize defects in free-standing bulk GaN substrates prepared by hydride vapor phase epitaxy. Melton KOH-NaOH (1:1) solution was found to be effective to produce etch pits on bulk GaN with density close to the anticipated dislocation density. Under preferred etching and measurement conditions, a strong correlation between CL mapping and selective-etching techniques for revealing defects in the bulk GaN was demonstrated. All structural defects causing etch pits are confirmed to be non-radiative recombination centers showing dark contrast in CL map, while CL mapping could give additional information about certain internal defects underneath the GaN top-surface. The clear correlation established in this comparative study provides strong support for the viability of using both techniques for evaluating bulk GaN. (c) 2006 Elsevier B.V. All rights reserved.