Disclosed are a thin film transistor including a substrate and a gate electrode, a gate insulating film, a semiconductor layer, a source electrode, and a drain electrode formed on the substrate and a method of fabricating the thin film transistor, wherein the gate insulating film is made of a high dielectric ternary material, A2-XBXO3, wherein A is any one selected from the group consisting of aluminum, silicon, gallium, germanium, neodymium, gadolinium, vanadium, lutetium, and actinium, B is any one selected from the group consisting of yttrium, lanthanum, zirconium, hafnium, tantalum, titanium, vanadium, nickel, silicon, and ytterbium, and A is an element different from B. The gate insulating film may be formed through a solution process, and a high-quality insulating film may be obtained through heat treatment at low temperature.