A semiconductor device including a horizontal unit semiconductor element, the horizontal unit semiconductor element including: a) a semiconductor substrate of a first conductivity type; b) a semiconductor region of a second conductivity type formed on the semiconductor substrate; c) a collector layer of the first conductivity type formed within the semiconductor region; d) a base layer of the first conductivity type having an endless shape and formed within the semiconductor region such that the base layer is off the collector layer but surrounds the collector layer; and e) a first emitter layer of the second conductivity type formed in the base layer, the horizontal unit semiconductor element controlling, within a channel region formed in the base layer, movement of carriers between the first emitter layer and the collector layer, wherein the first emitter layer is formed by plural unit emitter layers which are formed along the base layer.