The fabrication of high aspect ratio macropore arrays on p-type silicon under optimum anodization conditions is demonstrated. The depth of the macropore can reach 400 mu m with an aspect ratio of 100. The thickness of the pore wall is 1-2 mu m. Presence of cationic surfactant in the electrolyte protects the pore walls and promotes the growth of the unidirectional macropores. The shape of pre-etched pits is critical for the formation of high aspect ratio macropores on p-type silicon. A self-supported silicon membrane of straight-through macroporous channels has also been obtained.