PURPOSE: To prevent the influence of variations in a power source to be affected to other block such as a logic unit by individually connecting a circuit block and a power pad on the same semiconductor chip, supplying power from individual power sources, and isolating the wells formed in every block.

CONSTITUTION: Aluminum wirings La, Lb, Lc,... are connected from a power pad 1 to circuit blocks 2a, 2b, 2c,... and power voltage is applied to the wells 3a, 3b, 3c,.... The wirings La, Lb, Lc are respectively connected to the common lines 1a, 1b, 1c of the source electrodes of an FET in each block. Thus, when the voltage of the power source varies in the well 3b due to the operation of the logic unit 2b, the variation in the power source is transmitted to other blocks from Lb via the pad 1 and the other La, Lb, the influence is hardly affected, thereby improving the reliability of the circuit.