A distributed feedback semiconductor device is disclosed which has a diffraction grating disposed near a light emitting active layer, a double hetero structure with the active layer sandwiched between n- and p-type semiconductors and n- and p-side electrodes for injection a current into the active layer, one of the n- and p-side electrodes being divided into a plurality of electrodes, and in which a current is injected into the active layer across the n- and p-side electrodes for laser oscillation to obtain output light. A first current source is connected to each of electrodes into which one of the n- and p-side electrodes is divided, and a second current source is connected to the divided electrodes via resistors, for injecting a current into the active layer in a desired ratio. The first and second current sources are controlled in accordance with the light emitting state of the active layer. In operation, a current is injected into the active layer through the divided electrodes while controlling the injected-current density in the active layer to be uniform in the direction of travel of light until the injected current reaches a threshold current at which the distributed feedback semiconductor laser device starts to oscillate, and a current thereafter injected while controlling the injected-current density to be maximum in at least that region of the active layer in which the light intensity is maximum in the direction of travel of light.