A novel passivation film on GaAs surface has been grown by microwave sulfur glow discharge technique.Electronic properties of GaS/GaAs interface have been studied by C-V,I-V, and DLTS measurements.C-V measurement shows that the properties of GaS/GaAs interface are nearly ideal and interface state density is about 1012／（cm2·eV),which agrees with result from DLTS measurement.From leak current of MIS′s structure in I-V spectra,the resistivity of GaS is estimated about 1011Ω·cm.