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AlN was grown on r ‐ and c ‐plane sapphire substrates by low‐pressure hydride vapor phase epitaxy (LP‐HVPE). Nitridation and buffer methods were used and compared. Results show that the buffer method is appropriate for the growth of a‐plane AlN. In‐plane stresses were measured and found to be different in the two in‐plane directions parallel and perpendicular to the AlN c‐axis. In‐plane stress anisotropy is reduced at high temperature leading to a smoother surface, partly owing to a decreased difference in the growth rates between two in‐plane directions. However, too high a temperature decreases the crystal quality of a‐plane AlN. Thus, there exists an optimal temperature range for the growth of a‐plane AlN, in which improved crystal and surface qualities can both be obtained. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)