We have observed oscillations in the differential conductance as a function of the width of the tunneling barrier formed between the tip of a scanning tunneling microscope and a clean cleaved InP(110) surface. The oscillations were analyzed in terms of a simple model for a field emitted tunneling current that experiences a finite reflectivity at the InP(110) surface due to the step in the potential at the sample side of the tunneling barrier. Oscillations were not found at high bias in accord with the energy dependence of the reflectivity, and quantitative agreement was found between the model‐implied value of the surface work function and reported data. ©1995 American Institute of Physics.