ASA energy band calculation method. The results show that the origin of interface charge Qss is the rearrangement of valence electrons in the metal and semiconductor atomic layers at the metalsemiconductor interface. The formation mechanism of the interface charge Qss in this paper is similar to that of Tung's model of the polarization of the chemical bonds at metalsemiconductor interfaces. Both of them can account for the origin of interface charge Qss even at the monocrystalline metalsemiconductor interfaces.