A semiconductor device includes a substrate that includes a first active region, a second active region, and an isolation region. An isolation layer pattern fills a trench in the substrate. A first gate insulation layer pattern and a first gate, electrode structure are formed on the first active region. A second gate insulation layer pattern and second gate electrode structure are formed on the second active region. The first gate electrode structure includes a first polysilicon pattern, a second polysilicon pattern, and a first metal pattern. The second gate electrode structure includes a third polysilicon pattern, a fourth polysilicon pattern, and a second metal pattern. An upper surface of the isolation layer pattern is higher than upper surfaces of each of the first and third polysilicon patterns. A sidewall of each of the first and third polysilicon patterns contacts sidewalls of the isolation layer pattern.