We report the deterministic growth of individual single-crystal organic semiconductor nanowires of silver–tetracyanoquinodimethane (Ag–TCNQ) with high yield (>90%) by a vapor–solid chemical reaction process. Ag–metal films or patterned dots deposited onto substrates serve as chemical reaction centers and are completely consumed during the growth of the individual or multiple nanowires. Selective-area electron diffraction (SAED) revealed that the Ag–TCNQ nanowires grow preferentially along the strong π–π stacking direction of Ag–TCNQ molecules. The vapor–solid chemical reaction process described here permits the growth of organic nanowires at lower temperatures than chemical vapor deposition (CVD) of inorganic nanowires. The single-crystal Ag–TCNQ nanowires are shown to act as memory switches with high on/off ratios, making them potentially useful in optical storage, ultrahigh-density nanoscale memory, and logic devices.