The present invention relates to a semiconductor device having a multi-layered structure comprising an emitter layer, a base layer, and a collector layer, each composed of a group III-V n-type compound semiconductor in this order; a quantum dot barrier layer disposed between the emitter layer and the base layer; a collector electrode, a base electrode and the emitter layer all connected to an emitter electrode; the quantum dot barrier layer having a plurality of quantum dots being sandwiched between first and second barrier layers from the emitter layer side and the base layer side, respectively and each having a portion that is convex to the base layer; a base layer side interface in the second barrier layer, and collector layer side and emitter layer side interfaces in the base layer having curvatures that are convex to the collector layer corresponding to the convex portions of the quantum dots.