Cu can be deposited onto porous silicon (PS) by immersion plating from aqueous solution under open-circuit conditions. Oxidation of Si and reduction of Cu2+ ions are the coupled redox reactions during immersion plating. It is found that deposited Cu is dissolved again after a long-time immersion in the plating solution. The results from several measurements revealed that re-dissolution of Cu is attributed to the presence of dissolved oxygen. Because the standard potential of the reduction of oxygen is very positive, deposited Cu is oxidized. After the complete oxidation of PS is achieved, dissolution of Cu by dissolved oxygen becomes remarkable. (C) 2003 Elsevier B.V. All rights reserved.