A technique of phase identification from the characteristics of electronic structures is established by Auger electron spectroscopy. GaN epilayers in wurtzite and zinc-blende polytypes are used for practical investigations. Auger spectra show phase-dependent energetic shifts and peak intensity variations. Simulation of theoretical spectra reveals the substantial correlation of the Auger line shape with the bonding electronic states. This approach demonstrates the correspondence between electronic structure and atomic structure and hence provides criteria for phase identification.