We synthesized a new photo-patternable organic/inorganic hybrid material, polyhedral oligomeric silsesquioxane (POSS) derivative containing cyclohexene-1,2-epoxide functional groups (POSS-EPOXY), and fabricated an organic thin film transistor (OTFT) using pentacene as an active p-type organic semiconductor and POSS-EPOXY as a gate dielectric layer to demonstrate its applicability for organic electronics. The pentacene transistor with the POSS-EPOXY layer shows comparable transistor characteristics as that with the prototypical polymeric gate insulator of poly(vinylphenol) (PVP). They exhibit field-effect mobility of micro(FET) approximately 0.075 cm2/Vs, threshold voltage of V(T) = -22.2 V, the on/off current ratio of 7 x 10(5), and the subthreshold slope of 3.9 V/dec.