A semiconductor device is provided. The semiconductor device includes a substrate including a first region and a second region. First and second dielectric films are positioned above the substrate in the first region and the second region, respectively. First and second gate stacks are disposed on the first and second dielectric films, respectively. The first gate stack includes a first TiAlC film in direct contact with the first dielectric film, and a first barrier film and a first metal film sequentially stacked on the first TiAlC film. The second gate stack includes a first LaO film in direct contact with the second dielectric film. A second TiAlC film, a second barrier film, and a second metal film are sequentially stacked on the first LaO film.