There has been a search for alternative dielectrics with significantly increased dielectric constants, K, which increases physical thickness in proportion to K, and therefore would significantly reduce direct tunneling. However, increases in K to values of 15-25 in transition metal and rare earth oxides are generally accompanied by decreases in the conduction band offset energy with respect to Si, E-B, and the effective electron tunneling mass, m(eff), which mitigate gains from increased thickness. A novel technique, based on stacked dielectrics, is used to obtain the tunneling mass-conduction band offset energy product. When combined with optical measurements of tunneling barriers, this yields direct estimates of the tunneling mass. (C) 2004 Published by Elsevier B.V.