In this work, the application of advanced X-ray scattering methods to the study of mesoscopic and low-dimensional heterostructures is briefly reviewed. Semiconductor quantum wire arrays, periodically corrugated surfaces (surface gratings) and quantum dots are investigated by high-resolution double-crystal X-ray diffraction and high- and low-angle reciprocal space mapping. It is shown that high-resolution X-ray experiments can provide useful and accurate information or? the geometrical parameters and structural properties of low-dimensional semiconductor heterostructures.