A new ET-based cation radical salt alpha'-(ET)(2)H2F3 (ET: bis(ethylenedithio)tetrathiafulvalene) was obtained by an electrocrystallization method using a highly conductive ionic liquid (EMI)[F(HF)(2.3)] (EMI: 1-ethyl-3-methylimidazolium) as an electrolyte, and its structural, transport and magnetic properties were investigated. The salt shows the semiconducting behavior with an activation energy of 0.05-0.08 eV. Static susceptibility of 8.9 X 10(-4) emu mol(-1) at 300 K, in support of the transport behavior, is firm evidence of a Mott insulator.