Structural properties of InAs quantum dots grown on Si (100) substrate have been investigated with G-GIXD reciprocal space mapping. Although both the volume (37 nm in diameter) and the surface coverage (about 11 %) of the InAs dots are small, strong diffraction spots have been observed. To investigate the origin of the peak broadening, we compared the experimental data with structural factors calculated with FEM. We have found that the size of diffraction spots from the InAs dots is determined not only by their size and within-a-dot strain distribution, but also by the dot-to-dot strain distribution. (C) 2002 Published by Elsevier Science B.V.