In a rectifier in which button diodes are mounted in pairs as columns on bases which also constitute heat sinks, the connector connecting the diodes to the AC phase is made of a material which has high thermal and electrical conductivity. The columns are fastened to the base-heat sink by use of additional heat sink members which in turn are fastened to the base by bolts or screws. The latter are electrically insulating. The base-heat sink is star-shaped, the diode columns being mounted on the rays of the star. Preferably, the additional heat sink members have extensions which increase their effective cooling area.