To understand the details of etching-induced damage on a GaN surface, n-GaN crystals were plasma-etched with He and N2 gases. The etched surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (XAS) methods. The composition of the surface etched with He plasma changed significantly to being Ga-rich with the N/Ga ratio nearly equaling 0.4–0.5. The ratio of the surface etched with N2 plasma was about 0.6. The shape of the near-edge X-ray absorption fine structure (NEXAFS) of the N-K edge deformed with increasing gas pressure and processing time. The deformation can be explained by the increase in the band widths of a number of peaks in the NEXAFS spectra owing to the increase in the degree of structural disorder in the crystal. The increase in band width for the surface etched with N2 plasma was larger than that for the surface etched with He plasma. The above results can be explained with the model of the elastic energy transfer ratio of He+ and N2+ ions incident on the solid surface.