The interface roughness and the correlation of the interface roughness in solid-state multilayer systems is of major interest due to the characterisation of the performance of such systems with respect to transport processes, both electrical and optical. The measurement of these parameters and their replication through thin solid films provides a way to investigate the physical processes during the growth process also (e.g. MBE, MOVPE). The diffuse X-ray scattering in coplanar geometry is well suited to measure these parameters without destruction of the sample. Two-dimensional X-ray scattering patterns in reciprocal space (space map) are measured by reflection in the region of total reflection. The analysis of the diffuse part of the reflected radiation by simulation programs gives access to the essential information about the statistical parameters of the interfaces. Due to the large area illuminated during the measurement, the extracted parameters have a high statistical significance. The talk presents results obtained with a high-power rotating anode at PTB. The measurements were carried out on different multilayer structures prepared by MOVPE, MBE and sputtering. The results will be compared with simulation and AFM based data of the internal interface. (C) 2003 Published by Elsevier Science B.V.