A method of manufacturing a flash memory device that prevents generation of voids when forming an interlayer dielectric film. The method may include forming a gate on a semiconductor substrate, and then sequentially stacking a first dielectric film and a second dielectric film on the semiconductor substrate, and then forming a first spacer comprising a first dielectric film pattern and a second dielectric film pattern on sidewalls of the gate by performing a first etching process, and then forming source and drain areas in the semiconductor substrate, and then removing the second dielectric film, and then sequentially stacking a third dielectric film and a fourth dielectric film on the semiconductor substrate, and then forming a second spacer comprising the first dielectric pattern and a third dielectric pattern on the sidewalls of the gate by performing a second etching process, and then forming an interlayer dielectric film on the semiconductor substrate including the gate and the first spacer.