A photoinduced electrical conductivity switching is observed in the molecular conductor of alpha-[bis(ethylenedithio)tetrathiafulvalene](2)I-3 at different temperatures with different irradiation light intensities. The threshold voltage for the differential-negative-resistance effect appearing in the current-voltage characteristic curve decreases and increases, respectively, as the light intensity is increased and as the temperature decreases below the insulator-metal phase transition. The potential application of molecular conductor in bidirectional light-activated thyristor devices is demonstrated. (c) 2007 American Institute of Physics.