Solution-processed or printed n-channel field-effect transistors (FETs) with high performance are not reported very often in the literature due to the scarcity of high-mobility n-type organic semiconductors. On the other hand, low-temperature processed n-channel metal oxide semiconductor (NMOS) transistors from electron conducting inorganic-oxide nanoparticles show reduced-performance and low mobility because of large channel roughness at the channel-dielectric interface. Here, a method to produce ink-jet printed high performance NMOS transistor devices using inorganic-oxide nanoparticles as the transistor channel in combination with a 3D electrochemical gating (EG) via printed composite solid polymer electrolytes is presented. The printed FETs produced show a device mobility value in excess of 5 cm2 V−1 s−1, even though the root mean square (RMS) roughness of the nanoparticulate channel exceeds 15 nm. Extensive studies on the frequency dependent polarizability of composite polymer electrolyte capacitors show that the maximum attainable speed in such printed, long channel transistors is not limited by the ionic conductivity of the electrolytes. Therefore, the approach of combining printable, high-quality oxide nanoparticles and the composite solid polymer electrolytes, offers the possibility to fully utilize the large mobility of oxide semiconductors to build all-printed and high-speed devices. The high polarizability of printable polymer electrolytes brings down the drive voltages to ≤1 V, making such FETs well-suited for low-power, battery compatible circuitry.