Superheated steam is steam at a temperature higher than its saturation temperature. If saturated steam is heated at constant pressure, its temperature will rise, producing superheated steam. This may occur in a boiler/autoclave if saturated steam is exposed to a surface with a higher temperature such as a boiler wall.

The steam is then described as superheated by the number of temperature degrees through which it has been heated above saturation temperature.

Superheated steam and liquid water cannot coexist under thermodynamic equilibrium, as any additional heat simply evaporates more water and the steam will become saturated steam. However, under dynamic conditions some degree of superheating is often possible.

Superheated steam is not suitable for sterilization.

Superheated steam is used in steam locomotives to improve efficiency and is generated using a superheater.