Fabrication of patterned anodic aluminum oxide arrays using a dense layer of barrier aluminum oxide as the anodization mask is described. This fabrication process includes patterning of the aluminum film with a photoresist and brief anodization at a high voltage. The photoresist is then removed and the aluminum film is again anodized at a low voltage to grow porous aluminum oxide. Using this procedure, we are able to fabricate anodic aluminum oxide arrays on silicon wafers consisting of alternating regions of porous aluminum oxide and aluminum metal perpendicular to the silicon substrate. (C) 2004 The Electrochemical Society.