Tunneling currents in reverse-biased base-emitter junctions are investigated and analyzed. Guided by a simple analytic theory, shallow n<sup>+</sup>-p junctions are designed with a variety of different concentration profiles. Measurements of the de electrical characteristics indicate a significant Zener tunneling component in the reverse diode current. The appearance of tunneling is ascertained by the temperature dependence, which also allows a clear distinction of other current mechanisms. The sensitivity of the current to the details of the doping profile is theoretically explained in terms of the maximum electric field in the junction and verified by SIMS and C-V profiling techniques. The C-V data are analyzed in a novel way to obtain experimental data on the maximum electric field making the conclusions valid for any arbitrary junction. The implications of the presence of high electric fields in shallow junctions are discussed with respect to scaling bipolar transistors. Copyright © 1983 by The Institute of Electrical and Electronics Engineers, Inc.