Provided are a thin film transistor and a method of manufacturing the same. The thin film transistor includes: a gate electrode; source and drain electrodes spaced apart in a up and down direction from the gate electrode and in a horizontal direction from each other; a gate dielectric formed between the gate electrode and the source electrode and between the gate electrode and the drain electrode; and an active layer formed between the gate dielectric and the source electrode and between the gate dielectric and the drain electrode, wherein the active layer is formed of at least two zinc oxide thin layers doped with an element.