The application of porous silicon (PS) as a filter substrate in microstructured systems is a promising field of research. Based on this approach, metal-assisted chemical etching is applied to produce PS in a cheap and fast way. This simple and effective method enables the fabrication of PS with different morphologies, pore distribution, and thickness by varying the deposited metal type and thickness, and the Si doping type and level. The metal (Au, Pt) is sputtered in varied thicknesses on patterned p- or n- doped silicon wafers. The etching solution consists of an 1: 1: 1 mixture of HF: H2O2: EtOH. Etching time and temperature are varied showing a direct effect on the pore depth. To obtain a thin permeable porous Si layer, advanced silicon etching is used to microstructure the back side of the patterned wafer. Hence, the resulting PS layers turn to thin membranes,150 mm thick, maintaining the desired mechanical stability at enhanced gas-permeation rates and thus face a very auspicious career as gas diffusion substrates. © 2005 The Electrochemical Society. All rights reserved.