We observed new "thermo-coloration" of the surface layer of SmS film in which it turned from blue-black to gold after annealing at 650 degreesC for 1 h in vacuum. X-ray photoelectron spectroscopy (XPS) was applied to investigate the chemical state of SmS. This phenomenon is different from the previously reported works. The contribution of Sm3+ state dramatically increased upon annealing. This implied that SmS film changes from semiconductor phase to the metal one and Sm oxide. Consequently, it is suggested that new thermo-coloration of SmS film is caused by the phase transition from semiconductor to metal under the presence of Sm oxide. (C) 2003 Elsevier Science B.V. All rights reserved.