This paper suggests a new fabrication method for surface micromachining based on porous silicon formation followed by electropolishing. in contrast to its known use as a sacrificial layer, in this work, porous silicon will be employed as constitutive material tur free-standing. mobile microstructures. In one fabrication step, a layer of porous silicon can be generated and released by subsequent electropolishing of a buried layer. This porous silicon layer can be held at the borders as a membrane that is suspended over a cavity. Another technique allows it to be liberated and to stand up and form mobile 3D structures, like plates, which may be actuated. Different masking techniques will be discussed. This new surface micromachining technology for creating free-standing structures does not need sacrificial layers and offers new possibilities in micromechanics, microoptics and microfluidics. (C) 2000 Elsevier Science S.A. All rights reserved.