A method for manufacturing a display device includes forming a first gate metal wire on a substrate, forming a first insulation layer that covers the first gate metal wire, forming a second gate metal wire on the first insulation layer, forming a second main insulation layer that covers the second gate metal wire, forming a second auxiliary insulation layer on the second main insulation layer, forming an exposed portion of an upper surface of the second main insulation layer by polishing the second auxiliary insulation layer, and forming a first data metal wire on the second main insulation layer and the second auxiliary insulation layer.