We have reported previously on the fabrication, using x‐ray lithography, of Si metal–oxide–semiconductor field‐effect transistors (MOSFET’s) having channel lengths ranging from 60 nm to 5 μm. Devices with channel lengths of 75 nm showed electron velocity overshoot at 4.2 K. We have improved the mobility of the short‐channel MOSFET’s by implanting with B and then growing the gate oxide rapidly such that the concentration in the inversion layer is about 2×1016cm−3rather than the 5×1017cm−3used previously. A peak concentration of 2.2×1017cm−3occurs at a depth of 0.19 μm, where it prevents punchthrough by screening the field lines from the drain. With devices having channel lengths shorter than 100 nm we measured mean electron velocities at 300 and 77 K that exceeded 107and 1.3×107cm/s, the bulk saturation velocities at these two temperatures. The highest mean velocity measured at 77 K was 2.3×107cm/s.