X-ray analysis has been important for advanced understanding of many microelectronic materials. Examples described in this paper are drawn from work on metal conductor lines and on semiconductors. In situ studies of Al and Al(Cu) conductor lines by X-ray microbeam diffraction and fluorescence have been used to test models and to obtain key parameters for electromigration in polycrystalline metals and alloys. EXAFS and high resolution X-ray diffraction have given information about local strains, defect complexes and deformation potentials in studies of group III, IV, and V impurities in silicon. Real-time high resolution diffraction measurements of optically induced structural changes in GaAlAs:Sn and GaAlAs:Si have provided tests for structural models of the DX-center. Some of these examples illustrate advances in X-ray analysis made possible by high brightness synchrotron X-ray sources. (C) 2002 Elsevier Science Ltd. All rights reserved.