Abstract: The purpose of this paper is to deal with the controversy in the literature about the origins of the hexagonal-shaped etch pits in GaN epilayers formed by wet-chemical etching,and get a better estimation of dislocation densities.Intensive observations of GaN etching by molten KOH are focused on the morphology evolution during etching and the dependence of etching on time and temperature.It is the three-dimensional shape of etch pits that could be correlated with the dislocation type,instead of the size as many literatures presented,and polarity is found to be responsible for the formation of these different etch pit shapes.In addition,the needed etching time to reveal all the dislocations decreases with increasing needed temperature.A combination of the optimum etching condition and the proper microscopy measurement leads to a reliable evaluation of dislocation densities in GaN.