Abstract: Current leakage of the surface of GaAs and other Ⅲ-Ⅴ semiconductors arises great interest. The leakage has an important influence on characteristics and reliability of compound semiconductor devices and circuits. The current leakage is steeply raised on contaminated surface of GaAs by Na ion.The surface states can be decreased with sulfur passivation of GaAs field-effect trasistor（FET）. Inthis paper our recent developments in the above area is described.