In this paper the operation mechanism of ambipolar Si-nanowire (Si-NW) Schottky-barrier (SB) FETs is discussed in detail using temperature dependent current-voltage (I-V) contour maps. Thermionic and field emission mechanism limited the overall conduction behavior of ambipolar Si-NW SB-FETs with considerable SB-height. However, Si-channel dominant transports with phonon scattering mechanism occur even in the SB based device at a specific bias condition, where charge carrier injection is saturated with a very thinned SB. Temperature dependent transconductance (gm) behavior, TCAD simulation and extracted activation energy (Eae) maps also support the explained operation principle of ambipolar Si-NW SB-FETs.