A thin-film transistor array substrate and a display device are disclosed. The thin-film transistor array substrate includes a substrate, a gate electrode disposed on the substrate, an active layer, which opposites the gate electrode, has a first region and a second region having different thicknesses, and comprises at least a semiconductor material, a gate insulating film interposed between the gate electrode and the active layer, and a source electrode and a drain electrode, which are respectively in contact with the active layer.