Layers of monocrystalline silicon were used as a working electrode in a three-electrode electrochemical cell with platinum as reference electrode in order to carry out stain etching processes leading to the formation of porous silicon layers. The potential at which the corrosion process takes place was measured as a function of the concentration of the oxidizing agent, and the reaction order with respect to the nitrate concentration was found to be close to one. From the experimental results a mechanism is formed for the stain etching process and a model proposed for growth of the porous layer. (C) 2003 The Electrochemical Society.