PURPOSE: To simplify a vertical mode in an ordinary mode and to enable a stable single mode at high-speed modulation, by forming at least more than 3 kinds of periodic structures having respective pitch intervals in the clad layer facing the semiconductor layer to be changed to an active layer.

CONSTITUTION: The respective pitch intervals of periodic structures 6a and 6b formed in a clad layer facing a semiconductor layer to be changed to an active layer 4 are set around 2,300 at which the second mode of the AlGaAs system semiconductor laser is oscillated. These periodic structures 6a and 6b are formed by performing twice exposures of the resonators each half of which is masked, using the two flux interference exposure method, and applying the given etching to them. The areas having respective crystal compositions in a subclad layer 5 are arranged regularly at A intervals. The light waves passing through the active layer 4 are reflected according to the Bragg's reflection conditions. Consequently, the phases of the light waves are arranged and are laser-oscillated. And the wavelength is λB=mA/2nr (m=1, 2, 3,...) (nr is an effective refractive index in the subclad layer 5).