A thin-film transistor includes: an active layer having a first side and a second side opposing to the first side; a main gate electrode spaced from the active layer on the first side, and including a conductive material; an auxiliary gate electrode spaced from the active layer on the second side, wherein the auxiliary gate electrode includes a phase change material having a phase change temperature; the auxiliary gate electrode is configured to have a transition between insulating and conductive based on a temperature of the auxiliary gate electrode; and the main gate electrode and the auxiliary gate electrode are electrically coupled to each other when the auxiliary gate electrode is conductive.