Uncapped self-assembled InAs quantum dots (QDs) grown on InP (001) were studied by synchrotron x-ray diffraction. Reciprocal lattice mapping of the (004) InAs peak shows the strain relaxation behavior with InAs coverage and coalescence at various growth conditions. The aspect ratio (height/diameter) of QDs increases linearly with decreasing strain in QDs in the perpendicular direction before complete strain relaxation by dot coalescence and misfit dislocation generation. The full widths at half maximum of InAs (004) peaks can be used to extract the average height of InAs QDs, which is in good agreement with that directly obtained by atomic force microscopy. (C) 2003 American Vacuum Society.