GaAs is one of the most promising III-V semiconductor compounds due to the electronic properties as direct energy band gap and high mobility of its charge carriers. The technological importance is related to the applications in optoelectronics as lasers devices from AlGaAs-GaAs or solar cells operating at high concentration factor. A real GaAs surface is covered with a relatively thick layer(~nm) of native oxide, which is the origin of a high density of surface states pinning the surface Fermi level within the band gap of semiconductor [1,2]. The sulfur passivation technique is a promising way to achieve a surface with a reduced surface state density and as a consequence is the change of surface potential barrier on GaAs. The method presented in this work is the sulphur passivation by treating the semiconductor in sulphide solutions that combines both chemical and electronic passivation[1,3]. The sulphur treatment was carried out in two different solutions: pure ammonium sulphide (NH4)2S(50%H2O) and sulphur monochloride (s2Cl2) in carbon tetrachloride CCl4(1:10). There have been obtained monolayers of sulphides on n-GaAs(100) and n-GaAs(110) by drying the solutions in a spinner. The aspects of the passivated surface was investigate in SEM analysis, that putted into evidence a adherent thick layer sulphur compound with the presence of S signal identified in a EDS analysis. The XPS recorded spectra on the threated surface of n-GaAs was putted into evidence the signals of Ga(3d), As(3d) and S(2p) as a result of the modification of n-GaAs surface. This modification can be regard as a result of the chemical interaction of sulphur ions in the solution with the surface which as a result is a chemisorption process with the formation of Ga-S and As-S bonds. The passivation process is accompanied by a relevant reduction of surface recombination velocity that can be indicated by photoluminescence studies.