Semiconductor memory device

Inventive concepts relate to a semiconductor memory device. The semiconductor memory device comprising, a substrate comprising an NMOS region and a PMOS region, a first gate pattern disposed on the NMOS region of the substrate, and a second gate pattern disposed on the PMOS region of the substrate. The first gate pattern comprises a first high-k layer, a diffusion mitigation pattern, an N-type work function pattern, and a first gate electrode, which are sequentially stacked on the substrate, the second gate pattern comprises a second high-k layer and a second gate electrode which are sequentially stacked on the substrate, the diffusion mitigation pattern is in contact with the first high-k layer, a stacked structure of the first gate electrode is the same as that of the second gate electrode, and the second gate pattern does not comprise the N-type work function pattern.