Si3N4has been produced on GaAs with low interface trap densities by electron cyclotron resonanceN2–Heplasma assisted nitridation of a Si layer deposited on a GaAs (100) substrate. Nitridation at 150 and 400 °C was monitored by x-ray photoelectron spectroscopy (XPS) and produced stoichiometricSi3N4.The nitride layer thickness, as determined from XPS as a function of photoelectron takeoff angle, initially increased rapidly with nitridation time with a transition at a thickness of 12–18 Å to slower growth. Capacitance/voltage and conductance/angular frequency measurements were performed on metal-insulator-semiconductor capacitors fabricated from the nitrided samples. The results demonstrated interface trap densities with a minimum of3.0×1011 eV−1 cm−2when nitrided at 150 °C. At 400 °C the nitridation produced a poor quality interface, which resulted either from the higher temperature or from nitridation of all of the Si, leaving theSi3N4in direct contact with the GaAs.