Work function can be measured from the onset energy of secondary electron (SE) emission spectra in a scanning Auger microscope. In this article, the authors demonstrate the potential of such high spatial resolution work function spectroscopy in probing the Fermi-level position at semiconductor surfaces and the band bending at semiconductor interfaces. Using in situ cleaved cross-sectional GaAs and SiC p-n junctions, they show that the SE onset energy is very sensitive to the surface Fermi-level position and can also be used to measure electron affinity. By measuring the widths of the transition regions, the doping densities and built-in potential can be quantitatively obtained at a spatial resolution of similar to 10 nm. This technique can also be applied to a wide range of semiconductor heterojunctions. The influences of air cleaving, Ar ion sputtering, contamination, and primary electron beam are studied. They also discuss the advantages, limitations, and possible future improvements of this technique. (c) 2007 American Vacuum Society.