We report current versus voltage measurements as a function of temperature (I‐V‐T) and capacitance‐voltage (C‐V) measurements onn+‐GaAs/insulator/n‐GaAs capacitors where the insulators used are (i) AlAs and (ii) a GaAs:AlAs superlattice. For then+‐GaAs/AlAs/n‐GaAs structures activation energies of 0.38 eV are observed over the temperature range 100–300 K indicating that conduction takes place by thermionic emission through theX‐band states of AlAs. For the superlattice case a measured activation energy of ∼0.33 eV for thermionic emission has a contribution of ∼0.2 eV resulting from the band bending in the superlattice, as revealed by ourC‐Vmeasurements. We discuss the implications of these results for transport in superlattices and as a technique for determining miniband energies.