A thin-film transistor, a display device including a thin-film transistor, and a method of manufacturing a thin-film transistor are provided. A thin-film transistor includes: a base substrate, a semiconductor layer on the base substrate, the semiconductor layer including: a first oxide semiconductor layer, and a second oxide semiconductor layer on the first oxide semiconductor layer, the second oxide semiconductor layer having a Hall mobility smaller than a Hall mobility of the first oxide semiconductor layer, and a gate electrode spaced apart from the semiconductor layer and partially overlapping the semiconductor layer, wherein a concentration of gallium (Ga) in the second oxide semiconductor layer is higher than a concentration of gallium (Ga) in the first oxide semiconductor layer.