A modeling of reaction pathways in a TMAl/NH 3 /H 2 system including parasitic and polymeric reactions for computational simulations was constructed to study temperature and pressure dependences of growth rates and gas-phase chemistry in metalorganic vapor-phase epitaxial growth of AlN. AlN growth rates calculated were in good agreement with experimental data. Reactive molecules such as MMAlNH and Al–N became the major gas-phase species at the high-temperature range. With increasing pressure, the polymerization of these species was enhanced and AlN growth rate significantly decreased.