PURPOSE: To reduce the base resistance without deteriorating crystallization of a silicon by a method wherein an insulating film covering at least a part of an emitter region is extended to a base region encircling the emitter region with the width no exceeding 1μm.

CONSTITUTION: An n type epitaxial layer 2 with low impurity concentration is grown up to the thickness of 1∼20μm on an n type silicon substrate 1 to be a collection region with high impurity concentration. An oxide silicon film 10 is formed on the surface and then a part of the film 10 to be a base region is removed. A polycrystalline silicon film 11 is formed on overall surface and boron ion B+ is implanted in the film 11 by ion implanting process. After removing the film 11 excluding its part on the base region forming part, a nitride silicon film 12 is formed on overall surface. A base region 5 is formed by means of diffusing boron impurity doped in the film 11 in the layer 2. The films 12 and 11 on an emitter forming part in the resist 5 are selectively removed to make an opening 13 for implanting arsenic ion As+. An emitter region 8 may be formed by means of diffusing the ion As+ in the oxidizing atmosphere.