We report here that an ultra-thin oxide layer formed in the gate metal by plasma oxidation can serve the same role as self-assembled monolayer (SAM) dielectric, yielding the device performance similar to that for SAM-based organic thin film transistors. In addition, this simple plasma oxidation, unlike the case of SAM dielectrics, allows a smooth coating of the oxide dielectric with a thin (similar to 20 nm) polymer dielectric of poly (vinyl phenol) (PVPh). This organic transistor with the bilayer dielectric is robust. It has a subthreshold swing of 110 mV per decade, which is the best subthreshold voltage reported for an organic transistor.