The effects of (NH4)2Sx treatments on the interface traps in Au/n-GaAs and Au/n-In0.5Ga0.5P Schottky contacts are investigated by deep level transient spectroscopy measurements. The interface trap concentration in Au/GaAs increases when the residual S overlayer is sublimated after (NH4)2Sx treatments. But the trap concentration decreases when the S overlayer is rinsed by de-ionized water. In Au/InGaP, the phosphorus vacancy-related interface traps are passivated effectively by the (NH4)2Sx treatment. These results are attributed to the fact that S bonds with As but not with P. © 1997 American Institute of Physics.