Abstract A simple, effective, and universal model is presented for the formation of silicon nanowires during silver metal assisted chemical etching of silicon. The model explains nanowire formation in terms of well-known and well-understood principles of electrochemical exchange current densities at silver metal/solution interfaces, silicon/silver ion reaction kinetics, and diffusion limited aggregatoon (DLA) kinetics. The role of the metal in the formation of nanowires is clearly defined and the model is easily extended to other transition metal systems, including: Pt, Au and Pd.