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. © 1996 American Institute of Physics.