In order to investigate the physical limits of the metal-oxide semiconductor field-effect transistor (MOSFET), we have experimentally studied the non-stationary carrier transport in a high lateral electric field using the n- and p-channel silicon-on-insulator (SOI) transistors. We have experimentally demonstrated that the electron drift velocity ve shows velocity overshoot, that is, over 107 cm/s (1.2×107 cm/s) at room temperature, at less than 0.1-μm channel length Leff, which has been realized under suppressed self-heating conditions. The carrier velocity was obtained by measuring both the transconductance and the gate-to-source capacitance. Moreover, according to the experimental Leff dependence of the carrier velocity, the physical limit of both electron and hole velocity at Leff=0 is estimated to be about 2.5×107 cm/s, which indicates that the transconductance is equal to about 2000 mS/mm.