The interval .LAMBDA. between each stripe of interference fringe generated in a conventional n-type contact layer is determined by a function (f(.lamda.)=.lamda.(n.sup.2-n.sub.eq.sup.2).sup.-1/2/2) wherein .lamda., n, and n.sub.eq represent luminous wavelength .lamda. of lights radiated from a light emitting part 104, refractive index n of the n-type contact layer, and equivalent refractive index n.sub.eq of the n-type contact layer in guided wave mode, respectively. The remaining thickness .delta. of the n-type contact layer 102 at the concave part D which is formed at the back surface of the crystal growth substrate may be about .LAMBDA./2. When at least one portion of the n-type contact layer which is formed right beneath the laser cavity remains with about .delta. in thickness, the n-type contact layer arranged even right beneath the laser cavity can maintain excellent contact to a negative electrode. As a result, effective light confinement enables to adequately suppress ripples in FFP owing to lights leaked into the n-type contact layer, to thereby provide a semiconductor laser which oscillates stable lights.