A method of manufacturing a semiconductor device may include forming split gate structures including a floating gate electrode layer and a control gate electrode layer in a cell region of a substrate including the cell region and a logic region adjacent to the cell region. The method may include sequentially forming a first gate insulating film and a metal gate film in the logic region and the cell region, removing the metal gate film from at least a portion of the cell region and the logic region, forming a second gate insulating film on the first gate insulating film from which the metal gate film has been removed, forming a gate electrode film on the logic region and the cell region, and forming a plurality of memory cell elements disposed in the cell region and a plurality of circuit elements disposed in the logic region.