A semiconductor device includes a substrate, device isolation film defining an active region of the substrate in which a gate trench extends, a gate insulating film disposed along sides and a bottom of the gate trench, a gate electrode disposed on the gate insulating film in the gate trench and having a first portion, a second portion on the first portion, and a third portion on the second portion, a first barrier film pattern interposed between the first portion of the gate electrode and the gate insulating film, a second barrier film pattern interposed between the second portion of the gate electrode and the gate insulating film, and a third barrier film pattern interposed between the third portion of the gate electrode and the gate insulating film. The work function of the first barrier film pattern is greater than the work function of the second barrier film pattern and less than the work function of the third barrier film pattern.