PURPOSE: To resist a soft-error to α-rays, to thin an epitaxial laver and to increase working speed by forming an N-type buried layer to a P-type substrate, shaping a P-type buried layer into the buried layer and growing the epitaxial layer onto these substrate and buried layers.

CONSTITUTION: A first N-type buried layer 2 having high resistance and a deep junction and a second N-type buried layer 3 having low resistance and a shallow junction are formed in regions in which each of N channel type and P channel type transistors is shaped in a P-tyre substrate, and P-type buried layers 4 are formed to the layer 2 and a bipolar element isolation region. when an N-type epitaxial layer 5 is shaped onto these layers and a P-type well layer 6 is formed, the P-type well layer in the N channel transistor is formed to an insular shape surrounded by the N-type buried layer and the N-type epitaxial layer. and resists against a soft-error by α-rays while the P-type well layers are deepened substantially without thickening the N-type epitaxial layer by the layers 4 and withstanding voltage thereof is increased. A bipolar transistor is operated at high speed without lowering withstanding voltage by the thin N-type epitaxial layer.