A semiconductor laser of a refractive index-guided type comprises a GaAs (100) substrate having a mesa of (011) orientation thereon, a buffer layer grown on the top surface and side walls of the mesa of the GaAs (100) substrate and having a mesa on the top surface, a first cladding layer grown on the buffer layer in compliance with the outline on the top surface of the buffer layer having the mesa so that a mesa is provided, an active layer grown on the first cladding layer and separated on the side walls of the mesa of the first cladding layer, and a second cladding layer grown on the active layer, a boundary surface of which is in contact through a separated portion of the active layer with a boundary surface of the first cladding layer, wherein the first and second cladding layer are of a semiconductor material selected from AlGaInP and AlInP, and of a forbidden energy bandgap larger than that of the active layer. The semiconductor laser as described above is fabricated by a single etching process and a single and common metalorganic vapor phase epitaxy.