A mask assembly includes a first mask area including first opening areas, and a second mask area including second opening areas having centers located at vertices of virtual squares in a row direction and a column direction, half-etching areas having centers located at centers of the virtual squares, and a non-etching area surrounding the second opening areas and the half-etching areas. Each of the second opening areas includes a base portion and at least one protrusion portion protruding from the base portion.