Abstract: A microwave oven has a cooking chamber; a microwave window in one of the chamber walls; a glass-ceramic plate covering the window; a securing frame affixed to the chamber wall and immobilizing the plate by engaging peripheral portions thereof; a microwave connecting housing adjoining the window externally of the cooking chamber; a microwave generating and guiding device bounding at least in part the space defined by the connecting housing for directing microwave energy into the cooking chamber through the connecting housing and the window; and an electric resistance heater in the cooking chamber. A high-temperature resistant seal is interposed between the securing frame and the plate; the seal is bonded to the chamber wall and the plate. The space defined by the connecting housing is maintained at a pressure which is greater than that prevailing in the cooking chamber.