A brief review of silicon etching and electrochemistry provides an introduction to galvanic cell formation in silicon/metal contacts in aqueous electrolyte solutions. It is shown that such gal- vanic cells, which operate under open-circuit conditions, can be used to perform most of the functions of anodic etching and pas- sivation. Applications relevant to sensor fabrication are described. These include the control of surface morphology, etch-stop mech- anisms, and microporous and macroporous etching. In addition, surface structuring by open-circuit photoetching, a process which also depends on galvanic effects, is considered.