The steady-state surface concentration profiles of Cs ions during secondary ion mass spectrometry (SIMS) measurements were investigated in details for Si using low-energy oxygen primary ion bombardment. Depending on the bombardment conditions of Cs primary ions, there are shoulder regions or transient regions under the sputtered surface where Si secondary ion intensities are lower than those at bulk region. To achieve accurate depth profiling with minimum transient region using Cs primary ions, it is necessary to choose bombardment conditions such that primary ion energy is below 1 keV or large angle of incidence over 80degrees will be needed for higher primary ion energy. (C) 2002 Elsevier Science B.V. All rights reserved.