In this paper, we propose a simple, original and costless method to produce monocrystalline silicon sub-micron wires by electrochemical etching of silicon wafers. For this purpose, 30-50 Omega cm p-type silicon samples were etched in a HF (50 wt %):H2O:acetic acid (4.63:1.45:2.14) electrolyte applying various current densities. As the resulting material is made of macroporous silicon filled with mesoporous silicon, when a slight KOH or TMAH etching is performed, we are able to produce vertical wires with an aspect ratio up to 500. The thinnest measured wire diameters are about 200 nm for an average wire density above 10(7) cm(-2). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3592883] All rights reserved.