Electric-field thermopower modulation method is demonstrated in detail using SrTiO3-based field-effect transistor structure as an example. Using water-infiltrated nanoporous 12CaO center dot 7Al(2)O(3) glass "CAN" as the gate insulator, carrier electrons up to similar to 10(15) cm(-2) can accumulate within an extremely narrow 2D electron gas (similar to 2 nm), leading to an unusually large enhancement of thermopower. Our electric field-effect approach should be applicable to fully verify the performance of thermoelectric materials with complicated crystal structures. This approach may accelerate the development of nanostructures of high performance thermoelectric materials.