Abstract: In a cleaning process for removing parasitic depositions on surfaces of a process chamber of a CVD reactor, a susceptor of the CVD reactor is heated by a heating device, and the susceptor is regulated to a specified temperature or is heated with a constant heat output. Concurrently, an etching gas is supplied to the heated process chamber. The thermal response of at least one object is monitored, in which the thermal response is the temperature of the wide face of a process chamber cover, the wide face facing away from the process chamber. The parasitic depositions influence the emissivity of the surface of the process chamber cover, the emissivity influencing the temperature distribution in the process chamber. The supply of etching gas is terminated when the temperature reaches a comparison value, the temperature changing in response to changes in the surface emissivity during the cleaning process.