In this letter, we present an atomic-force-microscopy investigation of the Stranski–Krastanov growth of Ge on Si(100). Upon increasing the base width of the islands, two morphology transitions are found. The first transition occurs at a base width of ∼50–60 nm and marks the evolution from few-monolayer-thick terraces to square-base pyramidal islands. In the second transition, which takes place when the base width exceeds ∼300 nm, the island shape changes from square base pyramids to tetragonal truncated pyramids. Both transitions are brought about by the need for the system to minimize the elastic energy. ©1997 American Institute of Physics.