A detailed investigation of residual thermal stress and misfit strain in GaN epitaxial layers grown on technologically important substrates is performed. The thermal stress is low when GaN is grown on AIN, SiC and Si, and relatively higher when Al2O3 substrate is used. The stress is compressive for AIN and Al2O3 and tensile for Si and SiC substrates. Residual thermal stress analysis was also performed for three layer heterostructures of GaN/AIN/6H-SiC and GaN/AIN/AI(2)O(3). The stress remains the same when a sapphire substrate is used with or without an AIN buffer layer but reduces by an order of magnitude when a 6H-SiC substrate is used with an AIN buffer layer. (C) 2004 Kluwer Academic Publishers