The long-term target of producing all-organic devices requires custom-designed dielectric materials able to be applied and patterned with a wide range of new and fast deposition and patterning methods. Inorganic-organic hybrid polymers such as organic modified ceramics (ORMOCERs) have recently gained considerable attention in polymer electronics. Consisting of organically functionalized inorganic-oxidic units, their material properties can be tuned over a wide range and, in addition, their processing is very flexible providing good compatibility to many materials and substrates and allowing for direct patterning. A study on the application of different ORMOCER systems as gate dielectric layers in organic thin-film transistors (OTFTs) with pentacene as the organic semiconductor and directly structured contact holes is presented. Depending on the chemistry of the underlying ORMOCER system, different morphologies of the thermally evaporated pentacene were observed and correlated to the electrical characteristics of the transistor devices. In some cases, OTFTs with excellent electrical performance were achieved, showing intrinsic field-effect mobility values up to $1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$. Based on the high charge-carrier mobility of the pentacene-ORMOCER interface and the good dielectric, passivating, and patterning properties of the ORMOCER materials, these devices lay the foundation for a new generation of high-quality, fast, processable low-cost organic electronics.