A mask frame assembly manufactured via an extension-welding process on a stage, the mask frame assembly includes: a mask frame disposed on a stage, the mask frame including a first frame and a second frame having a first length, and a third frame and a fourth frame having a second length, the second length less than the first length. The mask frame assembly also includes a mask having respective ends welded and combined onto the first frame and the second frame. The first frame and the second frame include a slot disposed toward the stage, and at least portions of the first frame and the second frame corresponding to the slot are not in contact with the stage. The third frame and the fourth frame and the stage are in contact with the stage.