In the method of manufacturing a semiconductor device, according to the present invention, first, a dummy gate electrode consisting of a semiconductor layer and a non-metal cap layer formed on the semiconductor layer, is formed above a substrate. Then, diffusion layers are formed respectively on both sides of the dummy gate electrode. The dummy gate is used as a mask here, and thus the diffusion layers are self-aligned respectively with both sides of the dummy gate electrode. The formation of these diffusion layers requires a high-temperature heat treatment, however since the cap layer is made of a non-metal material, it is not melted down even in the high-temperature heat treatment. Next, the cap layer formed on the semiconductor layer is removed, and a gate groove made by the removal is filled with metal. Thus, a metal gate electrode made of a semiconductor layer and a metal layer is completed. As described above, in the present invention, first, a dummy gate electrode is formed of a non-metal cap layer, and the cap layer is removed after the formation of the diffusion layers, followed by filling the created gate groove with a metal. In this manner, the self-alignment of the diffusion layers and the metallization of the gate electrode can be achieved at the same time.