We propose a novel semiconductor laser structure. It is composed of three cascaded active sections: a Fabry-Pérot laser section sandwiched between two gain-coupled distributed feedback (DFB) laser sections. We have modeled this multi-section structure. The simulation results show that compared with index- and gain-coupled DFB lasers, a significant reduction in elongitudinal spatial-hole burning can be obtained with the proposed device, and this is what leads to a stable single longitudinal mode operation at relatively high optical power with a SMSR exceeding 56dB