Abstract: The invention relates to a plant for sintering or melting ceramic or refractory products in a wave-guide or a sounding cavity wherein they are subjected to the action of a microwave field, a plant wherein the temperature of the product to be processed is detected and the resulting signal compared with a reference value, so as to generate a differential signal or signal of error, and a driving electronic device to act, depending on said signal of error, on the value of the hyperfrequential power injected in the wave-guide or sounding cavity, in order to have the value of the signal of error reduced to zero.