The present invention refers to a method of regulating the steam superheating temperature in a circulating fluidized bed type gas cooler. Hot gas is introduced into a mixing chamber, where it is mixed with solids having a temperature lower than that of the gas, whereby the temperature of the mixing chamber settles to a mixing temperature. The mixture of the gas and solids is taken from the mixing chamber via a riser to a solids separator, heat being thereby cooling the mixture of gas and solids and transferring heat to heat transfer surfaces. Solids are separated from the gas in the separator and recirculated into the mixing chamber. In connection with the cooling of the gas, superheated steam is generated in evaporators and superheaters arranged in the cooler. The mixing temperature in the mixing chamber, according to the invention, is utilized for temperature regulation of the superheated steam generated in connection with the gas cooling. The mixing temperature may be regulated by controlling the amount and temperature of solid material being introduced into the mixing chamber.