A semiconductor laser includes a substrate having a principal surface; an active region disposed on the principal surface of a substrate, the active region including a quantum well structure, the active region having a top surface, a bottom surface facing the top surface, and side surfaces; an emitter region including a first semiconductor region of a first conductivity type on the top surface of the active region; and a collector region including a second semiconductor region of the first conductivity type on at least one side surface of the active region. The quantum well structure includes unit cells that are arranged in a direction of an axis intersecting the principal surface of the substrate.