The process for forming native sulfide films on p-PbSe layer (p-PbSe/CaF2//Si (111) structures obtained by molecular beam epitaxy (MBE)) by chemical and electrochemical sulfur treatments is described. These frequently used methods, have not yet been studied for PbSe layer passivation. X-ray photoelectron spectroscopy (XPS) measurements show the disappearance of carbon and oxygen contamination after sulfidation. A semi-quantitative analysis obtained from Auger electron spectroscopy (AES) spectra show sulfur and oxygen variation as a function of reagent concentration, sulfidation time, and applied potential. The thickness of sulfur penetration was estimated to be about 15 Angstrom for the chemical treatment and greater than 30 Angstrom for the electrochemical one. The surface morphology following these treatments was observed by atomic force microscopy. Annealing experiments show that a quasi-layer of PbS was formed on the PbSe surface. Chemical passivation and stability of the PbSe surface over a period of two months was demonstrated.