A rectifying region formed on the metal-semiconductor boundary. Metal-semiconductor as a whole has the same Fermi level in thermal balance. From semiconductors to metals, electrons need to overcome potential barriers. However, from metal to semiconductor, electrons are blocked by barriers, and with forward bias, the barrier on the semiconductor side decreases. On the contrary, when a reverse bias is applied, the barrier on the semiconductor side increases, so that the metal-semiconductor contact has a rectifying effect (but not all metal-semiconductor contacts). If the work function of metal is greater than that of semiconductor for P-type semiconductor, the work function of metal is less than that of semiconductor for N-type semiconductor. Moreover, when the impurity concentration of semiconductor is not less than 10 19/ cm3, ohmic contact will occur, and the barrier will not be rectified because of the high impurity concentration. When the semiconductor is uniformly doped, the width of the space charge layer of the Schottky barrier is consistent with the width of the depletion layer of the P-N junction with unilateral abrupt change.