The reverse-bias current–voltage characteristics of metal–oxide–silicon tunnel structures containing nonuniform ultrathin oxide layers are analyzed using a numerical three-dimensional quantum mechanical scattering calculation. We find that, in general, roughness at theSi/SiO2interface renders the oxide layer more permeable, but does not qualitatively alterI–Vcharacteristics. In the direct tunneling regime interface roughness induces lateral localization of wave functions which leads to preferential current paths, and is characterized by current densities which increase with island size. In the Fowler–Nordheim tunneling regime, however, interface roughness affects transport primarily through scattering, which increases with island size, and results in current densities which decrease with island size. We have also shown that appropriate one-dimensional models may be used to estimate the effect of interface roughness in limiting cases. ©1998 American Institute of Physics.