Process for fabrication of a micromechanical and/or nanomechanical structure comprising the following steps, starting from an element comprising a support substrate and a sacrificial layer: a) formation of a first layer, at least part of which is porous, b) formation on the first layer of a layer made of one (or several) materials providing the mechanical properties of the structure, called the intermediate layer, c) formation on the intermediate layer of a second layer, at least part of which is porous, d) formation of said structure in the stack composed of the first layer, the intermediate layer and the second layer, e) release of said structure by at least partial removal of the sacrificial layer.