A method for fabricating a suspended structure including a layer of membrane material over a substrate. The suspended structure overlies a cavity in the substrate. The method starts by generating a sacrificial layer comprising a first material that can withstand temperatures typically encountered in subsequent conventional semiconductor processing steps. In the preferred embodiment of the present invention, the bond between sacrificial layer and the underlying substrate must be capable of withstanding temperatures greater than the Si—Al eutectic point. A layer of membrane material is then deposited over the sacrificial layer. The membrane material comprises a second material different from the first material. An opening is introduced in the layer of membrane material thereby exposing the sacrificial layer. A first etchant is applied to the sacrificial layer through the opening until the sacrificial layer is removed leaving a portion of the cavity. The first etchant is chosen such that the first etchant removes the first material more rapidly than the second material. Finally, a second etchant is introduced into the cavity to expand the cavity. The second etchant is chosen such that the second etchant removes the substrate more rapidly than the second material. The first material is preferably PSG, thermal silicon dioxide, low temperature oxide, or tungsten.