A novel double-heterojunction PnpN optical thyristor is presented in which both the center n-layer and the center p-layer are completely depleted at equilibrium. This structure is an extremely attractive optoelectronic switch, because it allows the marriage of two usually incompatible features: speed and optical sensitivity. The speed results from the fact that our PnpN-structure can be reset to equilibrium, from any point on the current-voltage characteristics, in less than 10 ns by means of a simple negative anode-to-cathode voltage pulse. The optical sensitivity is a direct consequence of the center n- and p-layers being completely depleted of free carriers at equilibrium. We show experimental evidence of this reset operation by studying the dynamics of the free-carrier extraction from the center n- and p-layers.