A jet condenser of the type comprising a water chamber in a mixing chamber (24) and an after-cooler (52), wherein the water chamber is subdivided in a narrower upper water chamber portion (38a) and a broader lower water chamber portion (39b). The after-cooler (52) is fixed at the junction (66) of both water chamber portions (38a, 38b). Cooling water is injected into the mixing chamber (24) by nozzles (40) of the upper water chamber portion (38a) where it flows in vertical direction. By the reduced width of the upper water chamber portion (38a) flow resistance of steam flow in the mixing chamber (24) and, thereby, undesired subcooling is substantially diminished. (FIG. 3).