Abstract: A cooling system for a power module (or some other power electronics device) is described, the cooling system having a closed flow path for circulating a cooling fluid, the flow path having a pressure that is reduced to below atmospheric pressure. The cooling fluid is circulated along the flow path to provide cooling of the power module. The flow path is delimited from the exterior environment by a space provided between the flow path and the exterior environment, said space being sealed off from the cooling flow path, and said space being sealed off towards the exterior environment. The flow path has a pressure below atmospheric pressure and the space between the flow path and the exterior environment is evacuated and typically has a pressure lower than the pressure in the flow path.