A new semiconductor laser structure with digitally switchable wavelength is proposed. The device comprises two coupled c.avities with different optical path lengths, which form V-shaped branches with a reflective 2 × 2 half-wave optical coupler at the closed end. The reflective 2 × 2 coupler is designed to have a π-phase difference between cross-coupling and self-coupling so as to produce synchronous power transfer functions. High single-mode selectivity is achieved by optimizing the coupling coefficient. The switchable wavelength range is greatly increased by using Vernier effect. Using deep-etched trenches as partial reflectors, additional waveguide branch structures are used outside the laser cavities to form a complete Mach-Zehnder interferometer, allowing space switching, variable attenuation, or high speed modulation to be realized simultaneously. Detailed design principle and numerical results are presented.