Semiconductor device and fabrication method are provided. The method includes: providing a semiconductor substrate; forming initial fins on the semiconductor substrate; forming a gate structure material layer on the semiconductor substrate and the initial fins, the gate material layer having a top surface higher than the initial fins; forming a trench in the gate structure material layer and the initial fins, which passes through the initial fins along a direction perpendicular to an extending direction of initial fins and in parallel with a surface of the semiconductor substrate to form initial fins into fins; forming an isolation layer in the trench having a top surface higher than the fins; and forming gate structures on both sides of the isolation layer by etching the gate structure material layer.