Transistors, electronic devices including a transistor and methods of manufacturing the same are provided, the transistor includes an oxide semiconductor layer (as a channel layer) having compositions that vary in one direction. The channel layer may be an oxide layer including a first element, a second element, and Zn, which are metal elements. The amount of at least one of the first element, the second element, and Zn may change in a deposition direction of the channel layer. The first element may be any one of hafnium (Hf), yttrium (Y), tantalum (Ta), zirconium (Zr), gallium (Ga), aluminum (Al) or combinations thereof. The second element may be indium (In). The channel layer may have a multi-layered structure including at least two layers with different compositions.