We utilize an efficient, fully quantum mechanical approach to calculating ballistic transport in a fully depleted, silicon-on-insulator metal-oxide-semiconductor field-effect transistor in three dimensions to examine realistic devices with quantum wire channels. We find that, by including the atomistic nature of these small devices in the simulation, we observe variations in the threshold voltage dependent on the position of the dopants in the channel. Further, we find that the narrow channel access geometry creates a situation in which the impinging electron density in the source undergoes resonant tunneling in order to reach the drain end of the device. (C) 2004 American Vacuum Society.