A transistor includes a substrate having an active region defined by an isolation layer; a first trench defined in the active region and a second trench defined in the isolation layer; a fin region formed under the first trench; and a buried gate electrode covering sidewalls of the fin region and filling the first and second trenches. The buried gate electrode includes a first work function layer formed on the sidewalls of the fin region; a second work function layer formed on sidewalls of the first trench and the second trench; a third work function layer positioned over the fin region and contacting the second work function layer; and a low resistance layer contacting the third work function layer and partially filling the first and second trenches.