egion and a second conductivity type base contact region. The collector region is formed on a semiconductor substrate. The base region is formed on the surface of the collector region and in the vicinity thereof, and has a first impurity concentration. The emitter region is formed on the surface of the base region and in the vicinity thereof. The base contact region is formed on the surface of the base region and in the vicinity thereof, and has a second impurity concentration, higher than the first impurity concentration, for attaining contact with the base region. The base contact region and the emitter region are arranged at a prescribed interval while the base contact region extends toward the emitter region so that dispersion of values of a current amplification factor of the transistor is within a prescribed range.
According to this structure, the base contact region having a relatively high impurity concentration formed on the surface of the base region reduced in impurity concentration due to out diffusion of the impurity during the fabrication steps extends toward the emitter region for supplying a sufficient amount of the impurity to the base region as compared with the conventional semiconductor device. The base contact region and the emitter region are arranged at a prescribed interval for reducing dispersion of the base current, thereby reducing dispersion of the values of the current amplification factor of the transistor within the prescribed range.
As to the range of dispersion of the values of the current amplification factor, the value of average absolute deviation of the current amplification factor on five points in the wafer plane is preferably not more than 5 as a representative value.
If the value of average absolute deviation of the current amplification factor is not more than 5, it is conceivable that dispersion of the current amplification factor of the transistor is very small.
The prescribed interval between the base contact region and the emitter region is preferably at least 0.2 xce