X-ray diffuse scattering is used to probe size, shape, and strain distribution of self-organized SiGe/Si(001) islands, which were grown by liquid phase epitaxy. The SiGe islands show a truncated pyramidal shape with {111} side facets and a (001) top facet and they are highly uniform in size. With an averaged island base width of 130 nm and a corresponding height of 65 nm all the islands have a characteristic geometrical base-to-height aspect ratio of about 2. X-ray diffuse scattering is used to locally probe the elastically relaxed regions inside the island apex and the strongly strained regions near the substrate-island interface. It is found that the geometrical aspect ratio has a large impact on the x-ray diffuse intensity pattern in reciprocal space. By performing corresponding kinematical x-ray simulations this fact can be utilized to determine the aspect ratio with high sensitivity.