SEMICONDUCTOR DEVICE INCLUDING GATE STRUCTURE

A semiconductor device includes an active region, an isolation region on a side surface of the active region, a gate trench having a first trench portion crossing the active region and a second trench portion in the isolation region, a first gate portion within the first trench portion and a second gate portion within the second trench portion. The first gate portion and the second gate portion each includes a gate dielectric layer, a gate electrode on the gate dielectric layer, partially filling the gate trench, and having an upper surface disposed on a level lower than an upper end of the active region, and an insulative capping pattern on the gate electrode. The first gate portion includes a lower region, an intermediate region on the lower region, and an upper region on the intermediate region. A maximum width of the intermediate region is greater than a maximum width of the lower region and greater than a maximum width of the upper region.