Microstructural evaluation of thick (In,Mn)As epitaxial films grown by molecular‐beam epitaxy on InAs/GaAs(100) substrates is carried out by transmission electron microscopy (TEM). Films grown at the substrate temperature ofTs=300 °C show the inclusion of MnAs crystallites in the zinc‐blende host matrix, in which two types of crystallite morphologies, rod and approximately round shapes, are identified. In contrast, the MnAs crystallites are not observed in films grown atTs=200 °C, and TEM studies confirm that the films are primarily of zinc‐blende structure. Microstructural defects in the films are also discussed to assess the quality of epitaxy.