A nuclear microprobe with 400 keV helium ions has been used to characterize GaAs layers locally etched by focused laser irradiation in a wet chemical solution. A comparison of crystallinity between the side-walls and cleaved surfaces of etched grooves has been made using channeling contrast analysis. Degradation of surface crystallinity in channeling contrast mapping was observed at the side-walls etched by laser chemical processing at higher laser powers, which was found to be due to surface roughness arising from etching selectivity for GaAs at surface regions.