We fabricated laterally confined GaAs–AlGaAs superlattices with diameters between 500 nm and 2 &mgr;m. With decreasing device diameter, a gap evolves in the current–voltage curve around zero bias and steps show up at the onset of the current. This behavior is interpreted in terms of Coulomb blockade, a depletion of the center of the superlattice, and single-electron tunneling through donor levels. ©1998 American Institute of Physics.