We report galvanic deposition of Si onto 6061 Al alloy from dilute aqueous hydrofluoric acid (HF) at pH 2.5. The overall reaction involves reduction of SiF62- to Si with simultaneous oxidation and dissolution of Al. The Si film is about 12 mu m thick after 6 h of deposition. High resolution scanning electron microscopy shows that these Si films are nanoporous, with pore sizes ranging from 3 to 8 nm. The nanoporous Si films oxidize rapidly upon sample emersion. Elemental analysis by energy dispersive X-ray spectroscopy demonstrates that the as-deposited film contains 1-3 atom % Al, 3-6 atom % Cu, and 90-95 atom % Si. We believe that this is the first report of electrochemical deposition of Si thin films that does not involve organic solvents or molten salt electrolytes. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3521290] All rights reserved.