An elemental Sb layer, formed at the oxide/GaSb interface, causes large surface leakage current and recombination, which are two main drawbacks of GaSb-based devices in full photoelectric application. The proportion of elemental Sb to other Sb compounds at the GaSb surface was increased by immersing the sample into diluted HCl solution. With sulfuring of the GaSb surface, elemental Sb was replaced by Sb2S5 and Sb oxides were removed. The mechanism that prevents formation of the leakage path at the as-etched GaSb surface is elucidated by X-ray photoelectron spectroscopy (XPS).