A semiconductor device includes a first gate pattern and a second gate pattern on a substrate, the first gate pattern and the second gate pattern being spaced apart from each other, and a separation pattern that separates the first gate pattern and the second gate pattern from each other. The first gate pattern includes a first high-k dielectric pattern and a first metal-containing pattern on the first high-k dielectric pattern, the first metal-containing pattern covering a sidewall of the first high-k dielectric pattern. The second gate pattern includes a second high-k dielectric pattern and a second metal-containing pattern on the second high-k dielectric pattern, and the separation pattern is in direct contact with the first metal-containing pattern and spaced apart from the first high-k dielectric pattern.