The present invention pertains to an amplification device for a high-frequency signal. The invention is particularly adapted for the transmission of radiofrequency signals used for television of radio under frequency modulation. The amplification device for a high-frequency signal comprises of two amplification stages arranged in series, the first amplification stage being formed of a semiconductor preamplifier, the second amplification stage being formed of an electron tube cooled by the circulation of a fluid, the electron tube being arranged inside an enclosure intended to receive it. The semiconductor preamplifier is arranged in the enclosure and the preamplifier is cooled by the circulation of the fluid. The electron tube comprises a collector needing to be cooled by the circulation of the fluid, and the fluid circulates around a cooling circuit, in which the collector is connected in parallel with the preamplifier.