The present invention relates to a semiconductor laser which oscillates in a single longitudinal mode and with a low threshold current and which exhibits a good mode stability against reflected light, and provides a structure of a distributed feedback semiconductor laser with modulation for a gain. The structure is such that gain producing regions are periodically arranged and that a substance transparent to laser radiation is buried between the regions. A layer including the gain regions is formed of a superlattice layer, and an impurity is diffused or implanted into periodic positions of the layer, whereby the transparent regions and the gain regions with little lattice damages can be readily formed.