The chemical etched and (NH4)2S-treated InSb(lll) surfaces have been studied using Auger electron spectroscopy and X-ray phctoelectron spectroscopy. It is found that after etching in the CP-4 solution the InSb surfaces are covered by a native oxide overlayer in which the amounts of Sb oxide are obviously more than In oxide. The native oxide layer on the InSb surfaces is completely removed by sulfide treatment and then a sulfide passivation layer forms on the sample surfaces.