Anodic porous alumina films with thickness in the range of 20 to 50 nm were fabricated on a silicon substrate by electrochemistry, for use as templates for silicon nanopatteming and quantum dot growth. The atiodization conditions were investigated in detail and it was found that they differ significantly from those used to grow thicker films. Much lower electric fields were necessary, since the strong electric field causes fast dissolution of the grown alumina. Anodization was done in sulfuric or oxalic acid aqueous solutions. Due to the low anodization voltage used, high density of pores was achieved. By using the optimum anodization conditions found, anodic porous alumina films on silicon with small diameter high density vertical pores homogeneously distributed in the film were fabricated and characterized by transmission electron microscopy. (c) 2006 Elsevier B.V All rights reserved.