A photopatternable and solution-processable thin gate dielectric for organic thin-film transistors has been fabricated here using an organosiloxane-based organic - inorganic hybrid material. Incorporation of a UV-sensitive functional group allowed us to directly obtain a high-resolution patterned gate dielectric using conventional photolithography. Uniform distribution of ZrO2 nanoclusters increased the dielectric constant of the hybrid material from which the hydroxyl groups were removed by low-temperature heat treatment. Coplanar-type organic thin-film transistors utilizing the hybrid dielectrics showed a low threshold voltage and nearly no shift in the threshold voltage due to their high capacitance and the absence of the hydroxyl groups.