The aim of the invention is a device for coolant cooling in a gas turbine which, with a relatively simple construction and low plant complexity permits a particularly high degree of efficiency in using the heat produced on cooling the coolant from a gas turbine. Said aim is achieved, whereby a number of interconnected evaporator tubes for a flow medium, are arranged in a coolant channel, connected to a gas turbine, to form forced throughflow steam generator. Said device is preferably used in a gas and steam unit with a waste heat steam generator on the exhaust gas side of a gas turbine, the heating surfaces of which are connected into the water-steam circuit of a steam turbine. The evaporator tubes of the device are thus connected on the inlet side by means of supply line to the feed water train of the water-steam circuit of the steam turbine.