Grazing-incidence small-angle scattering (GI-SAXS) technique was applied to self-assembled Ge islands capped with Si. GI-SAXS has a merit over TEM and AFM that the structure of islands buried in a cap layer for stabilization can be evaluated nondestructively. By analyzing the scattering patterns, the size of Ge islands was estimated to be about 5 nm in height and 26 nm in diameter, with the islands density of 4.2 X 10(14)/m(2). From the best fitting of two-dimensional model intensity to the experiments, the shape of the islands was deduced.