PURPOSE: To eliminate the restriction to a layout by removing any influence of noise by surrounding and shielding the side and bottom of a current wiring with a conductive material whose one end is connected to a low impedance point.

CONSTITUTION: A shielding plate comprising a phosphor-doped polycrystalline silicon layer 1 is inserted between a semiconductor substrate 4 and a high impedance wiring 2. Further there is formed a shielding plate on both sides of the high impedance wiring 2 by providing aluminum conductors 8 on both sides of the high impedance wiring 2 and connecting the aluminum conductors 8 and the phosphor-doped polycrystalline silicon layer 1 through a contact region 3. Hereby, another wiring can freely be provided in the vicinity of the high impedance wiring 2 to eliminate the restriction to a layout.