PURPOSE: To manufacture a semiconductor device in high integration whose operational speed of a bipolar transistor is notably accelerated by a method wherein a collector electrode is formed of a polycrystalline Si layer in higher impurity concentration than that of an emitter electrode while collector diffused regions are composed of impurity diffused layers in high concentration than that of an emitter diffused region.

CONSTITUTION: Within a semiconductor device wherein an emitter electrode 7 and a collector electrode 8 comprise polycrystalline Si layers, the impurity concentration contained in the polycrystalline Si layer comprising the collectcr electrode 8 is higher than that contained in polycrystalline Si layer comprising the emitter electrode 7 likewise the impurity concentration of collector diffused regions 9b, 10 formed by the diffusion from the polycrystalline Si layer comprising the collector electrode 8 is higher than that of emitter diffused region 8a formed by the diffusion from the polycrystalline layer comprising the emitter electrode 7. For example, after forming the emitter electrode 7 and the collector electrode 8 by forming the same polycrystalline Si layers, As or P in high concentration is selectively ion-implanted in the collector electrode 8 and then further heat-treated to form an npn type bipolar transistor.