A CVD reactor may include a susceptor, process chamber and heat dissipation body. In the CVD reactor, one or more layers can be deposited on one or more substrates. The susceptor is heated by a heating devices. Heat is transported from susceptor, through a process chamber towards the process chamber ceiling, through the process chamber ceiling, and from the process chamber ceiling through a gap space to the heat dissipation body. The temperature of the process chamber ceiling is measured at at least two different azimuth angle positions about a central axis of the process chamber. The radial distance of the respective measurement points or zones from the central axis of the process chamber may be equal to one another. The at least two temperature measurement values are used to produce an average value or a difference value.