Abstract: It is an object of the present invention to provide a highly efficient semiconductor laser unit having excellent temperature characteristics, in which electrons or holes are suppressed from overflowing from the active layer to the cladding layers while the threshold of current density is maintained low. The present invention is to provide a semiconductor laser unit fundamentally composed of an active layer and cladding layers in which the active layer is interposed between the cladding layers the semiconductor laser unit comprising: a multiquantum barrier layer including well layers and barrier layers disposed between the active layer and the cladding layers or disposed in the cladding layers close to the active layer, wherein the well and barrier layers have a high reflectivity with respect to the electrons and holes at a position close to .GAMMA.