A high-κ zirconium oxide gate dielectric is fabricated using a solution-based process at room temperature. UV irradiation decomposes and oxidizes a zirconium-based gel film, which densifies into an ultrathin (<10 nm) dielectric, providing high areal capacitance and low leakage current when passivated with a SAM. Polymeric transistors are fabricated on the gate dielectric entirely at room temperaure and operate with gate swings below 3 V, displaying high mobility (0.2 cm2 V−1 s−1)