PURPOSE: To realize a bipolar transistor having high performance without increasing a depth of a base in the step of thermally oxidizing after a gate electrode of a MOS transistor and an external base electrode of the bipolar transistor are formed.

CONSTITUTION: An N-P-N type bipolar transistor and a P-channel type MOS transistor are formed on a P-type silicon substrate. An external base electrode 24A of the bipolar transistor and a gate electrode 24B of the MOS transistor are formed of the same film containing P-type impurity. A laminated film of a silicon oxide film 20 and a silicon nitride film 19 exists at least partly between the substrate and the electrode 24A. That is, in the step of thermally oxidizing after the gate electrode and the base electrode are formed, the base region is covered with the silicon nitride film, and hence a depth of a base diffused layer is not increased.