A cooling capsule for a thyristor wherein the capsule is provided with a metallic core having at least one heat transfer surface and with a plurality of bores extending between surfaces of the core so as to form a meander-line-like flow path therethrough between an inlet opening and an outlet opening. The aforesaid surfaces between which the bores extend are provided with recesses each of which connects adjacent pairs of bores and the capsule is further provided with plate-like members, each of which covers a recess and is joined thereto by electron beam welding.