Vertically aligned Si nanowires were fabricated utilizing a metal-assisted chemical etching scheme using a thin anodic aluminum oxide (AAO) template formed on (100) Si substrate. The diameter and length of the obtained Si nanowires were about 55 and 340 nm, respectively, when the thickness of the AAO template was about 600 rim. The diameters and shapes of the Si nanowires were determined by the hole size and shape of the Ag mesh on the AAO template. In addition, the lengths of the vertical Si nanowires depended on both the AAO thickness and the Ag film thickness. (C) 2010 American Vacuum Society [DOI: 10.1116/1.3336572]