Magneto-conductance oscillations in a periodic magnetic field have been observed in a GaAs/Ga_0.77Al_0.23As heterojunction. The oscillations occur in a recently reported condensed phase of the two-dimensional electron gas and are attributed to magneto-oscillations of the phase transition temperature, similar to those seen in superconductors. This behaviour is one of several similarities to superconductivity which suggest that a superconducting transition may occur in this system. Transition temperatures as high as 10 K have been observed.