THIN FILM TRANSISTOR

Provided is a thin film transistor including a gate electrode, a semiconductor layer, a gate insulating layer provided between the gate electrode and the semiconductor layer and formed of an organic polymer compound, and a source electrode and a drain electrode provided in contact with the semiconductor layer and connected via the semiconductor layer, on a substrate, in which the content of metals selected from Mg, Ca, Ba, Al, Sn, Pb, Cr, Mn, Fe, Ni, Cu, Zn, and Ag in the gate insulating layer is 10 ppb to 1 ppm in terms of total amount, or the content of non-metal ionic materials selected from halogen ions, sulfate ions, nitrate ions, and phosphate ions is 1 ppm to 100 ppm in terms of total amount.