Schottky-barrier (SB) transistors show great potential as advanced transistors for meeting power, performance, area, and cost requirements. In this study, the dominant transport mechanisms of SB Si-nanowire (NW) transistors were investigated with respect to channel length for accurate performance estimation and to provide key insights for practical applications. Evaluations of the temperature-dependent drain current, transconductance, and activation energy from SB Si-NW transistors revealed that the SB-dominant thermionic effect competes with Si-NW channel-limited conduction when the initial SB height is relatively low. Moreover, the Si-NW channel length was sufficiently long to dominate the total resistance, overcoming resistance effects arising from the SB.