This paper describes the transmission electron microscope (TEM) investigations of the defect structure present at various FeAl/AlAs/GaAs interfaces. Although a systematic study has not yet been completed it is shown that by changing the growth temperature from 200°C to 300°C the growth morphology changes significantly. In-situ RHEED studies show the growth mode changes from layer-by-layer to island-like when the growth temperature is increased. TEM in both plan-view and cross-sectional modes is used to confirm these results. It is found that by increasing the growth temperature from 200°C to 300°C the growth mode switches from layer-by-layer (2D) with a continuous FeAl film, to island-like (3D) with significant numbers of “pin-holes”. A Moiré-fringe analysis is applied to determine the Burgers vector of the misfit dislocations. In both cases the interface between the FeAl and AlAs consists of a grid of misfit dislocations with  and  line directions whose Burgers vectors are  and  respectively.