A procedure and set-up for high-precision determination of the true surface temperature of wafers during growth by metalorganic vapour phase epitaxy is described. The reflectance of the surface measured by an EpiRAS(R) sensor is used for correcting the signal of a pyrometer for changes in emissivity. This allows for determination of the true surface temperature with a precision of +/- 1degreesC even for multilayer structures. This high precision allows to determine differences in the temperature of wafers of different size or rotating at different speed in an Aixtron Planetary Reactor(R). (C) 2002 Elsevier Science B.V. All rights reserved.