A horizontal semiconductor device having multiple unit semiconductor elements, each of said unit semiconductor element formed by an IGBT including: a semiconductor substrate of a first conductivity type; a semiconductor region of a second conductivity type formed on the semiconductor substrate; a collector layer of the first conductivity type formed within the semiconductor region; a ring-shaped base layer of the first conductivity type formed within the semiconductor region such that the base layer is off said collector layer but surrounds said collector layer; and a ring-shaped first emitter layer of the second conductivity type formed in said base layer, wherein movement of carriers between the first emitter layer and the collector layer is controlled in a channel region formed in the base layer, and the unit semiconductor elements are disposed adjacent to each other.