The minority‐carrier lifetime inn‐type GaAs‐on‐sapphire structures has been measured by transient laser‐induced photoluminescence. Single‐ and double‐heterojunction structures grown by organometallic vapor phase epitaxy have been examined and yield values of lifetime between 0.1 and 0.4 ns. Transmission and scanning electron microscopic analyses of layers show that the best surfaces and lowest defect densities resulted from isothermal growth at 690 °C. Threading dislocations in the range of 5×107to 6×108cm−2are observed in GaAs grown on (0001)‐oriented sapphire substrates.