A quantum cascade semiconductor laser includes a substrate and a semiconductor region provided on a principal surface of the substrate, the semiconductor region including a mesa waveguide, a first burying region provided on a first side surface of the mesa waveguide, and a second burying region provided on a second side surface of the mesa waveguide. Each of the first and second burying regions includes a plurality of laminate regions and a plurality of bulk semiconductor regions that are alternately arrayed. The laminate regions are separated from each other by the bulk semiconductor regions. The bulk semiconductor regions are provided on side surfaces of the laminate regions so as to embed the laminate regions. Each of the laminate regions includes a semiconductor laminate structure having a plurality of semiconductor layers.