As a result of the exposure to solution of different crystallographic facets during anisotropic etching of three-dimensional structures in silicon, the open-circuit potential of the semiconductor can change markedly. Using a (100)Si substrate, masked to reveal (111) facets, we show that such a shift in potential can alter the chemical etch rates of the individual facets. The extent of the changes depends both on the facets exposed and on their relative areas. Because the surface geometry, and with it the silicon potential, change continuously in time, chemical etching must adapt continuously to these changes. This is an interesting example of a self-regulating system with a complex feedback mechanism. The effects described in this work clearly influence anisotropic etching ratios and are therefore important for the fabrication of microelectromechanical systems. (C) 2004 The Electrochemical Society.