A thin film transistor, a method of manufacturing the same, and a display device including the same, the thin film transistor including a substrate; a polysilicon semiconductor layer on the substrate; and a metal pattern between the semiconductor layer and the substrate, the metal pattern being insulated from the semiconductor layer, wherein the polysilicon of the semiconductor layer includes a grain boundary parallel to a crystallization growing direction, and a surface roughness of the polysilicon semiconductor layer defined by a distance between a lowest peak and a highest peak in a surface thereof is less than about 15 nm.