PURPOSE: To enhance performance, to reduce cost and to easily integrate with a bulk semiconductor device by forming a base region and an emitter region by injecting and diffusing second conductivity type impurity and first conductivity type impurity by using the same impurity injection mask.

CONSTITUTION: A silicon oxide film 11 is formed on a polycrystalline silicon film 2 by thermally oxidizing or a CVD method of the film 2, and a base diffusing window 11a is opened by a photoetching method. With the film 11 as a mask P-type impurity such as boron is doped by an ion implanting method from the window 11a and annealed to form a P-type region 4a which becomes a base region. The film 11 is again opened with a collector diffusing window 11b by a photoetching method. A photoresist film 12 is formed partly in the window 11a to become a base contact region by photolithography technique. An N-type impurity 13, such as phosphorus, arsenic is ion implanted from the windows 11a, 11b.