A MESFET structure, grown by Si‐MBE, with a very sharp, degenerate Sb‐doped layer serving as conducting channel is presented. Particular care was taken to prevent clustering of the dopants, which is monitored by TEM. The lateral concentration profile of a locally doped sample was determined by SIMS. From uniformly doped samples, a mesa‐etched transistor structure was prepared. The channel current was controlled by a Schottky gate. The output characteristics of the field‐effect device were measured at 4.2 K.