Since its discovery in 1956, porous silicon has found various applications according to its wide range of morphologies (chemical sensing structures, Micro-Electro-Mechanical Systems-MEMS, silicon based optoelectronics, etc.). In this paper, we present a macroporous material, with pore diameters larger than 1 mu m, produced in a polarized HF/H2O mixture ([HF]=4.5 wt.%). Some square apertures were realized in a highly doped poly-silicon deposited on a thin (300 nm) silicon oxide layer. Then, electrochemical etching of the N-type (100 oriented silicon with total current densities of 5.65 and 7 mA/cm(2) during 2 h were performed with a backside illumination. We observed deep trenches near the mask border, perpendicular to the surface, over 120 mu m from the surface of the poly-silicon. Current density distributions have been simulated in two-dimensional structures in order to explain these phenomena. (C) 2005 Elsevier B.V. All rights reserved.