Undoped aluminum nitride films were grown on 4H or 6H silicon carbide substrates, using metal–organic chemical-vapor deposition at 1150 °C. Different growth conditions were used, and two different V/III ratios were tested. Metal–insulator–semiconductor capacitors were made for high-frequency capacitance–voltage measurements at room temperature, from which the film thickness was determined. Accumulation, depletion, deep depletion, and inversion were seen for the best films, which also displayed peaks in x-ray diffraction rocking curves. Although large flatband voltage shifts occurred, indicating a fixed charge and interface trap problem, low conductance was observed. A flow of ammonia during ramp-up was found to improve the AlN films. © 1997 American Institute of Physics.