The present invention discloses a tunable semiconductor laser based on half-wave coupled partial reflectors. The laser comprises two resonant cavities; one resonant cavity is mainly composed of an optical waveguide, a first partial reflector and a second partial reflector, and the other resonant cavity is mainly composed of an optical waveguide, a first partial reflector and a second partial reflector. The resonant cavities are arranged along the same straight line and coupled to each other, and the two second partial reflectors in the two resonant cavities are connected by a common coupling waveguide. The present invention has the best single-mode selection, and an emitted wavelength can be switched between a series of channels; an optical grating needs not to be manufactured, and the structure is simple; and the laser has a high degree of freedom in coupler design and a great manufacturing tolerance and can realize large-scale digital tuning.