a wavelength tunable semiconductor laser includes an active region including an active layer generating an optical gain by injection of a current , a phase control region including a tuning layer generating variation of a refraction index by injection of the current , and a distributed bragg reflector region including a tuning layer generating variation of a refraction index by injection of the current . the active region , the phase control region and the distributed bragg reflector region are arranged in alignment in a resonance direction . a diffraction grating is provided in the vicinity of the tuning layer of the distributed bragg reflector region . the wavelength tunable semiconductor laser includes a device for uniformly injecting a current to the phase control region and the distributed bragg reflector region . the optical confinement factor to the tuning layer of the phase control region is greater than an optical confinement factor to the tuning layer of the distributed bragg reflector type .