A novel semiconductor laser which can achieve mode-hop-free tuning is proposed. The device consists of an etched diffraction grating (EDG) as a dispersive element to provide the mode selection function and an active waveguide to provide optical gain for the laser. The slab waveguide region of the EDG contains a tuning section covered by an electrode to inject a tuning current

and thus changes the refractive index. Mode-hop-free tuning is achieved by specially designing the shape of the tuning section

so that the tuning rate of the central wavelength reflected by the EDG and the tuning rate of the resonant wavelength of the laser cavity are equal. An optimized tuning section shape is designed to obtain the largest tuning range within a limited current range. Numerical simulation is presented to demonstrate the mode-hop-free tuning operation.