We fabricated an n-channel accumulation-type field-effect transistor (FET) on a SrTiO3 single crystal having a polyvinyl alcohol (PVA) layer and a Na+-doped PVA layer as a gate insulator. Both devices show an n-type FET performance having a response time of 10-100 second order. This slow response is due to the gradual formation of an electric double layer by solvated Na+ ions moving through the water absorbed in the PVA layer towards the surface of SrTiO3 by applying a gate voltage (V-G), which is manifested by the fact that Na+-doping into the PVA layer dramatically reduces the driving voltages and the response time. In these devices, metallic or semiconducting behaviors are observed if the applied V-G is large enough to form a conducting channel during cooling of the devices. These results indicate that electrons are certainly doped into the surface of SrTiO3 by applying V-G in both devices. (C) 2009 Elsevier B.V. All rights reserved.