We fabricated an electrochemical field-effect transistor (FET) of octathio[8]circulene (1) thin-film, deposited on interdigitated array electrodes, and operated it with a gate dielectric layer of an ionic liquid (N,N-diethyl-N-methyl(2-methoxyethyl) ammonium bis(trifluoromethylsulfonyl)imide) electrolyte. The FET performance, obtained by the alternating current method for the source-drain current measurements, revealed a high carrier mobility of 2.4 x 10(-2) cm(2)/Vs and a very low-power operation. The threshold potential for the on-state was nearly half of the oxidation potential of 1. (C) 2009 Elsevier B.V. All rights reserved.