The electron‐mirror microscope (EMM) has been used to study photosensitivenpn‐type junctions in heat‐treated epitaxial PbS films. The EMM indicated variations in junction symmetry and strength on a much smaller scale than previously observed with a light‐spot scanning technique. In addition, the variations observed were found to correlate with surface topography. Regions of high junction density that have nearly zero photovoltaic response due to cancellation effects, were clearly resolved with the EMM.