We report two processing techniques to sandwich a thin (tens of nanometers) GaAs layer between ferromagnetic metallic electrodes. Such devices are valuable in the study of the spin properties of electrons in semiconductors. In these processes an AlAs layer is selectively etched from underneath a GaAs/NiFe/Au heterostructure using hydrofluoric acid. Subsequently, the rest of the structure which comprises GaAs/NiFe/Au is inverted in such a way that the GaAs layer lies on the top of the NiFe layer. The mean roughness of the inverted GaAs surface is 1.2 nm and it is crack free. In the first process, structures with an area of tens of microns are inverted on the same chip. In the second process, small disks with an area of a few microns are inverted on a different host chip. (C) 2003 American Vacuum Society.