To provide a thin-film transistor capable of controlling the gradation of an organic LED device by discretely controlling the current level, a method for manufacturing the thin-film transistor, an array substrate including the thin-film transistor, a display device and a driving system therefor.

This thin-film transistor includes a plurality of insulating layers 16, 24 formed on an insulating substrate 10 and on both opposite sides of the active layer 18 interposed between them, a first and a second gate electrodes 12 and 14 formed adjacent to these insulating layers 16 and 24, and wirings 38a and 38b connected to the first and the second gate electrodes 12 and 14 respectively for independently controlling the potentials of the first and the second gate electrodes 12 and 14. The area S1 of the first gate electrode 12 is different from the area S2 of the second gate electrode 14, and the current level can discretely be controlled in four levels.