In accordance with various embodiments of the disclosed subject matter, an organic thin film transistor, and a fabricating method thereof are provided. In some embodiments, the method for forming an organic thin film transistor (OTFT), comprising: forming a transparent gate layer on a transparent base substrate; forming a first initial silicone polymer layer on the transparent gate layer; and performing an oxidization process to partially oxidize the first initial silicone polymer layer to form a gate insulating layer, including an oxidized inorganic sub-layer that contacts the transparent gate layer, and a non-oxidized organic sub-layer.