A stack of a plurality of alternating heat emitting devices and evaporating units, wherein the heat emitting devices comprise power electronic components and wherein at least one of the evaporating units is arranged for cooling at least one of the heat emitting devices by evaporation of a cooling fluid, the at least one evaporating unit comprising: - at least one thermo-conducting wall (42a, 42b) that is thermally connectable to the at least one heat emitting device; - a first inlet channel adapted for receiving the condensed cooling fluid from a condenser; - a first fluid distributor fluidly connected to the first inlet channel for receiving the cooling fluid therefrom, and having a volume for collecting the cooling fluid therein; - a first plurality of evaporation channels each having a first end and a second end, the first ends being fluidly connected to the first fluid distributor for receiving the cooling fluid therefrom, the first plurality of evaporation channels being in thermal contact with the at least one thermo-conducting wall (42a, 42b) such that in an operating state the cooling fluid is heated in the first plurality of evaporation channels by the heat from the at least one heat emitting device and thereby at least partially vaporized and driven out from the first plurality of evaporation channels at their second ends; - a first fluid collector fluidly connected to the second ends of the first plurality of evaporation channels for receiving the evaporated cooling fluid therefrom, and having a volume for collecting the evaporated cooling fluid therein; - a first outlet channel fluidly connected to the first fluid collector and adapted for receiving the evaporated cooling fluid therefrom; wherein the at least one thermo-conducting wall (42a, 42b) has a cooling surface portion, the cooling surface portion being defined as the minimum convex surface portion enclosing all projections of the first plurality of evaporation channels onto the at least one thermo-conducting wall (42a, 42b), and wherein the first inlet channel is positioned in the evaporating unit such that its projection on the at least one thermo-conducting wall (42a, 42b) is situated outside the cooling surface portion, such that in the operating state the cooling fluid inside of the first inlet channel is pre-heated by the at least one heat emitting device before entering the fluid collector. - at least one thermo-conducting wall (42a, 42b) that is thermally connectable to the at least one heat emitting device; - a first inlet channel adapted for receiving the condensed cooling fluid from a condenser; - a first fluid distributor fluidly connected to the first inlet channel for receiving the cooling fluid therefrom, and having a volume for collecting the cooling fluid therein; - a first plurality of evaporation channels each having a first end and a second end, the first ends being fluidly connected to the first fluid distributor for receiving the cooling fluid therefrom, the first plurality of evaporation channels being in thermal contact with the at least one thermo-conducting wall (42a, 42b) such that in an operating state the cooling fluid is heated in the first plurality of evaporation channels by the heat from the at least one heat emitting device and thereby at least partially vaporized and driven out from the first plurality of evaporation channels at their second ends; - a first fluid collector fluidly connected to the second ends of the first plurality of evaporation channels for receiving the evaporated cooling fluid therefrom, and having a volume for collecting the evaporated cooling fluid therein; - a first outlet channel fluidly connected to the first fluid collector and adapted for receiving the evaporated cooling fluid therefrom;