In situ characterization techniques are necessary tools in modern MOCVD equipment within both the research and production environments. In this paper, we describe two recently developed in situ devices for high-speed rotating disk MOCVD systems: (1) an emissivity-compensated pyrometer and (2) a deflectometer. Emissivity-compensated pyrometry provides accurate temperature measurements during epitaxial growth, where dynamic changes in emissivity occur due to the changing deposits on the carrier and wafers. In situ deflectometry allows real-time measurement of wafer curvature (bowing), resulting from strain caused by lattice-mismatch and spatial temperature gradients. The deflectometer also provides carrier warpage measurements, along with tilt angle of wafers relative to the carrier. Both devices can measure the spatial profile of reflectivity across individual wafers, and determine the resulting growth rate, layer thickness, and composition. We will discuss the concepts and techniques behind these in situ tools, along with providing examples of their application to the development and production of GaN-based light emitting diodes. (C) 2004 Elsevier B.V. All rights reserved.