PURPOSE: To obtain a large number of longitudinal modes by forming partial irregularities to a side wall constituting the difference of refractive indexes for controlling a lateral mode in the direction parallel with an active layer and partially reflecting a lateral mode advancing in the direction of an optical axis.

CONSTITUTION: An N-Al0.35Ga0.65As clad layer 202, an Al0.05Ga0.95As active layer 203, an Al0.35Ga0.65As clad layer 204 and an N-GaAs cap layer 205 are formed on an N-GaAs substrate 200, to which a groove 201 is bored, in succession through a liquid phase growth method. The groove 201 is buried flatly with N-Al0.35Ga0.65As at that time. Striped selective Zn diffusion is made reach to the P-Al0.35Ga0.65As clad layer 204 from the surface of the N-GaAs cal layer 205. Consequently, a P type Zn diffusion region 206 can be formed. A P type ohmic electrode 207 of Au/Pt/Ti is formed on the surface of the cap layer 205 and an N type ohmic electrode 208 of Au-Ge-Ni on the surface of the N-GaAs substrate 200 respectively. When currents are flowed in the forward direction, a laser oscillation is generated in an active layer 209 on the groove 201.