Wurtzite-type aluminum nitride (h-AIN) films were epitaxially grown on off-asis Si (111) substrates by electron-cyclotron-resonance plasma-enhanced metalorganic chemical vapor deposition (ECRMOCVD) using trimethylalminum (TMA) and ammonia (NH3) as source gases. Plasma space potential in the growth chamber was lowered by setting the magnetic field distribution as a mirror field. For the growth of h-AlN with excellent crystallinity on Si substrates, nitridation of the substrate surface, growth of a low-temperature (LT) buffer layer, and epitaxial growth of AlN films were performed under a min-or field condition in a growth chamber. Thermal nitridation at 1050 degrees C prior to the epitaxial growth appreciably improved the crystallinity of AW films. The growth of buffer layer at temperatures below 650 degrees C was not so effective for the improvement of the crystallinity and crystal orientation of AIN epitaxial layer. The proportion of domain including stacking Faults and that whose c-axis was parallel to the substrate surface was very small (I-(0002)/(I(10-11) + I(10-11)) > 700), irrespective of the gas feed ratio of N source to Al source (NH3/TMA) during the epitaxial growth process. Under a small gas feed ratio (NH3/TMA < 200), however, the diffraction peak intensities from the non-epitaxial domains became large.