A novel method for the formation of ap+‐layer underneath a Si(111)7×7 surface is presented. It is based on annealing of an epitaxial Al/n‐Si(111) interface up to complete desorption of the Al film. This leads to a strong potential variation within the substrate, as observed in Si‐2pcore‐level photoemission spectra with variable sampling depth, while scanning‐tunneling microscopy reveals an unchanged 7×7 reconstructed surface. These observations are consistent with ap+doping of (4±2)×1018/cm3and a lowering of the surface Fermi level by (0.06±0.02) eV. ©1995 American Institute of Physics.