Abstract: A ceramic or refractory product is placed in a sounding cavity close to but spaced from an opposing member and they are heated to a predetermined temperature to sinter or melt said product by subjecting them to the action of a hyperfrequential electromagnetic field. The opposing member is formed from a material having dielectric losses higher than those of said product in the temperature range below said predetermined temperature so that the intensity of the field will be increased locally in the immediate vicinity of the surface area of said product opposed to said member and that area will be exposed to thermic radiation from the opposing member and be protected by that member from thermic losses.