The surface phosphidization and bull; hydrogenation for GaAs on Si has been realized simultaneously using the phosphine (PH3)-added H-2 plasma-exposure schemes. The PH3/H-2 plasma-exposed GaAs Schottky diodes showed significant increase in reverse breakdown voltage (V-br), which was believed to be due to the deactivation of dislocation-related deep levels. By the incorporation of phosphorous (P) atoms, the plasma-induced damages were effectively suppressed, and the passivated GaAs Schottky diodes on Si showed a good thermal stability.