Macropore formation in prepatterned p-type silicon was conducted. Pre-etch pits with 4 x 4 and 1 x 1 mu m were prepared before anodization of silicon. Using the prepatterned silicon, the effect of applied current density on the ordering of macropores was investigated. The pattern size and the current density greatly affected the pore formation behavior. The ordering and disordering of macropores formed in p-type silicon were discussed by taking account of the electric field in silicon. The distortion of the electric field near the pre-etch pits depended on the size of the pre-etch pits. The effect of applied current density on the pore formation was explained by the gradient of the electric field or the local current distribution near the growing fronts. On the basis of this understanding, silicon nanowire formation was also demonstrated. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3256126] All rights reserved.