The charging effect of n- and p-type layers of silicon under oxygen ion bombardment in an SIMS instrument was used to explore the possibility of determining the p/n junction depth. Complex ions like Si2O4 or Si2O5 (negatively charged) were recorded because of their narrow energy distributions and, hence, their sensitivity to changes of the surface potential. In the case of a p/n junction, a characteristic shift of the surface potential, as seen in the Si2O5 intensity profile, coincides with the depth of the metallurgical junction. In the case of an n/p junction, though, the marked intensity change is short by 250 nm of the metallurgical junction depth and appears to coincide with the onset of the depletion zone. (C) 2002 Elsevier Science B.V. All rights reserved.