  We present magnetotransport measurements on freely suspended two-dimensional
electron gases from AlGaAs/GaAs heterostructures. The technique to realize such
devices relies on a specially MBE grown GaAs/AlGaAs-heterostructure including a
sacrificial layer. We fabricated simple Hall-bars as well as quantum cavities
and quantum dot systems. We find well-pronounced Shubnikov-de Haas oscillations
and observe commensurability resonances, allowing characterization of the
electron gas in these 100 nm thin membranes.
