Abstract: The distributed reflector includes a substrate and at least one optical waveguide formed on the substrate and having a refractive index larger than the substrate and at least one optical confinement layer having a refractive index smaller than the optical waveguide layer. A diffractive grating is formed in at least one layer constituting the optical waveguide. The diffractive grating has a structure of which at least one parameter defining optical reflectivity varies depending on its position, and is formed continuously for at least two periods, the period being approximately defined by the length of repeating unit region. The parameter may be pitch, coupling coefficient, bandgap composition, phase shift, etc. The semiconductor laser includes the distributed reflector which may be of a distributed reflector type or distributed feed back type and has distributed reflector regions and a phase adjustment region.