Secondary ion mass spectrometry (SIMS) was used for characterizing the depth distribution of small amounts of alloying elements in three different copper-based dilute alloys, i.e., copper-chromium, copper-iron, and copper-nickel-silicon alloys. The samples were annealed at high temperatures under a low oxygen partial pressure. The SIMS depth profiles revealed that oxygen penetrated the copper-based alloys, and chromium and silicon were enriched on the surface side so as to form oxides during annealing. On the other hand, chromium and silicon were depleted beneath the enriched surface layer. However, the depth profile of iron was similar to that of copper. These phenomena were likely to be correlated with the reactivity of the alloying elements with oxygen. The formation kinetics of the depleted zones of chromium and silicon has been discussed on the basis of the selective oxidation of these alloying elements. (C) 2008 Elsevier B.V. All rights reserved.