A glow discharge technique is used to grow native oxides and oxyfluorides on GaAs. The capacitance-voltage and conductance-voltage measurements of the resulting metal/insulator/semiconductor structures show vastly different properties. Specifically, the density of interface states in the d.c.-to-5 MHz range appears to be much lower at the oxyfluoride interface than at the oxide interface. Secondary ion mass spectroscopy analyses indicate that some fluorine ions are mobile and the fluorine concentration is reduced by about an order of magnitude after a thermal anneal at 450°C. X-ray photoemission studies indicate that the glass is a mixture of GaF 3 and AsOF 3 molecules.