CdSe quantum dots on ZnSe, grown by molecular beam epitaxy and formed during reorganization of an initially uniform film by thermal activation, are microstructurally elucidated in cross section and plan view, using transmission electron microscopy. In diffraction contrast, an almost uniform wetting layer is clearly visible. Dark contrast features with a distinctly larger extension into growth direction mark the location of quantum dots. Individual quantum dots can be identified in high-resolution imaging both by lattice expansion and contrasts arising from their strain fields. Plan-view images show the coexistence of two classes of quantum dots with an average lateral size of⩽10 nm(area density100 &mgr;m−2) and 10–50 nm(20 &mgr;m−2),respectively. The shape of the larger entities is pyramidlike. ©1998 American Institute of Physics.