We present magnetotransport measurements on freely suspended two-dimensional electron gases from AlxGa1-xAs/GaAs heterostructures. The technique to realize such devices relies on a specially molecular beam epitaxy grown GaAs/AlxGa1-xAs-heterostructure, including a sacrificial layer. We fabricated simple mini-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.