Abstract: A heating system for an HF oscillator.The system comprises a reentrant cavity (10) controlling an UHF oscillator and sized to generate an UHF electric field with a frequency F much higher than the resonance frequency F.sub.Q of the piezoelectric crystal (50) of the HF oscillator which itself is located in the space between the central core (14) and the bottom (12) of the cavity and in such a manner that the two electrodes (34,35) of the oscillator are respectively located substantially in the planes of the free end of the central core (14) and of the inside of the bottom (12) of the cavity (10). The electrodes (34,35) are located in bores (16,15) in the conducting parts of the cavity in such a manner that the peripheral part of each electrode is surrounded at close proximity but without making contact with the wall of the corresponding bore (16,15). The electrodes (34,35) are connected to an HF oscillator by insulated leads (24,25).