Abstract: In a semiconductor device including a bipolar transistor having a base region formed in a collector region, and an emitter region formed in the base region, the emitter region comprises a high concentration region in contact with the base region, and a low concentration region provided between the base region and the high concentration region. The low concentration region is formed by introducing an impurity with a mask including a large opening. In addition, the high concentration region is formed by introducing an impurity with a mask including a small opening.