Investigations of misfit dislocations in the mismatched GaInP/GaAs heterostructures were conducted by transmission electron microscopy (TEM). Ga-rich and In-rich mismatched GaInP films having various compositions in the group III sublattice were prepared on (0 0 1) GaAs substrates by metalorganic chemical vapor deposition. Plan-view TEM studies show that most of the misfit dislocations preferentially lie along <1 1 0> directions in the GaInP/ GaAs heterointerface. In addition to the 60degrees mixed-type dislocations having Burgers vectors lying on (1 (1) over bar 1) or ((1) over bar1 1) planes, sessile-type dislocations with Burgers vector lying on (0 0 1) plane were also identified. TEM analyses show that pure edge dislocations are formed through the interactions of those 60degrees mixed-type dislocations in both Ga-rich and In-rich mismatched GaInP/GaAs heterostructures. (C) 2003 Elsevier Science B.V. All rights reserved.