We experimentally investigate the miniband transport in a novel kind of superlattice fabricated by the "cleaved edge overgrowth" method. The structure represents a field effect transistor, where the channel consists of an MBE-grown superlattice perpendicular to the current flow. By means of the gate the Fermi energy can be adjusted between the bottom of the first miniband and into the minigap. We observe pronounced negative differential resistance at electric fields across the superlattice as low as 160 V/cm. From magnetotransport measurements a relation between the applied gate voltage and the position of the Fermi energy in the artificial band structure is established. Electron mobility depending on the Fermi energy: is deduced separately from Shubnikov-de Haas oscillations, from the voltage at the peak current and from the low-field resistance. (C) 2000 Elsevier Science B.V. All rights reserved.