To provide a manufacturing method of a semiconductor device including a bipolar transistor which can operate at high speed by forming an oxide film between an intrinsic transistor part and a collector extraction part under appropriate control, and has excellent characteristics at high frequency by reducing parastic capacitance between the passive component and the substrate.

In this manufacture of a semiconductor device, a field oxidation is performed under the state that a single crystal silicon film 3 having a high dopant concentration is exposed in the region other than where a transistor is formed, and a single crystal silicon epitaxial film 21 having a low dopant concentration is partially left in the separation region between the intrinsic transistor part 15 and the collector extraction electrode part 16. Hereby, an element separating oxide silicon film 12 around the transistor part, and a separating oxide silicon film 17 between the intrinsic transistor part 15 and the collector extraction electrode part 16, are simultaneously formed in one process.