We realize a nonvolatile and rewritable memory effect in an organic field-effect transistor (OFET) structure using polymethylmethacryrate (PMMA) dispersed with 10-methyl-9-phenylacridinium perchlorate (MPA(+)ClO(4)(-)) as a gate dielectric. Applying a voltage between a top source-drain electrode and a bottom gate electrode induces electrophoresis of two ions of MPA(+) and ClO(4)(-) towards the corresponding electrodes in the memory devices. The drain currents of the memory devices markedly increase from 10(-9) A to 10(-2) A under no gate voltage condition due to the strong space charge polarization effect. Our memory devices have excellent electrical bistability and retention characteristics, i.e. the memory on/off ratio reached 10(7) and the drain current maintained 40% of the initial value after 10(4) s. (C) 2009 Elsevier B.V. All rights reserved.