We propose and experimentally demonstrate a widely tunable coupled-cavity semiconductor laser based on a novel half-wave bow-tie coupler. The laser comprises two resonate cavities connected through the bow-tie coupler consisting of two back-to-back corner reflectors connected with a short waveguide, which produces a half-wave cross-coupling phase with an optimum coupling coefficient for achieving high mode selectivity. No complex grating or multiple epitaxial growth is needed. By tuning a single electrode at a fixed temperature, 29.6 nm wavelength tuning covering 38 channels with 100 GHz frequency spacing is achieved experimentally, with a side-mode suppression ratio of over 35 dB.