A digital circuit portion (6) and an analog circuit portion (7) are formed in a surface portion of a semiconductor substrate (4). A via (20) is formed in a region between the digital circuit portion (6) and the analog circuit portion (7). The via (20) extends through the semiconductor substrate (4) from a front surface to a back surface thereof, and is made of a dielectric (2) having its surface covered by a metal (1). The metal (1) is grounded. Signal interference between the analog circuit portion (6) and the digital circuit portion (7) is reduced by the via (20).