Abstract A Totally Light Controlled Static Induction Thyristor is described in this paper concentrating on the optical direct/indirect triggering and quenching mechanisms. Up to the present time, using two GaAs infrared LEDs ( λ = 880 nm , T r = 12 ns ), 300V - 1.7A is directly triggered and quenched in a turn-on time of 1.9μs and a turn-off time of 6μs, 540V - 1A is indirectly triggered and directly quenched in a turn-on time of 545ns and a turn-off time of 7.15μs, and 400V - 1A is indirectly switched in a turn-on time of 630ns and a turn-off delay time of 660ns.