A filamentary structure has been used to compare the electrical properties of a germanium surface with those of an adjacentp‐njunction intersecting the same surface. Surface charge is varied by field effect plates in the isolated portion of the filament and near the junction. An orderly relation can be found between surface potential variations and changes in the reverse currents across the junction. At low bias, the junction current varies with surface recombination velocity, and for bias near breakdown, the breakdown voltage varies with induced charge at the surface. For inverted surfaces, the low bias current varies rapidly as expected from channel length variations. With inverted surfaces, channel growth leads to large reverse current variations with surface potential, but breakdown voltage becomes independent of surface charge. These variations are considered in terms of simple theory, and device implications are discussed.