A semiconductor device including a device isolation layer defining an active region; a first trench in the device isolation layer; a second trench in the active region; a main gate electrode structure filling a portion of the first trench and including a first barrier conductive layer and a main gate electrode; a pass gate electrode structure filling a portion of the second trench and including a second barrier conductive layer and a pass gate electrode; a support structure filling another portion of the second trench above the pass gate electrode; a first capping pattern filling another portion of the first trench above the main gate electrode; and a second gate insulating layer extending along a bottom and sidewall of the second trench, wherein the second barrier conductive layer is between the second gate insulating layer and the pass gate electrode and extends along a bottom and sidewall thereof.