A double-heterostructure semiconductor laser is disclosed which has a semiconductive substrate of a first conductivity type made of III-V compound semiconductor material, a first semiconductive cladding layer of the first conductivity type disposed above the substrate, an active layer made of a semiconductor film provided on said cladding layer to serve as a light emission layer, and a second semiconductive cladding layer of a second conductivity type provided on the active layer to define a light waveguide channel of the laser. The second cladding layer is made of a compound semiconductor containing indium, phosphorus, and aluminum. A contact layer section is provided on the second cladding layer to cover the light waveguide channel. The contact layer is made of a compound semiconductor material containing gallium and arsenic, and has a band gap discontinuity at a boundary region of the light waveguide channel to form a barrier which serves to effectively seal current carriers in the waveguide channel, while the laser is emitting a laser light. This contact layer may also serve as a current-blocking layer.