A heat exchanger (1, 1') of a loop thermosyphon type comprising: a base plate with a first surface for receiving a heat load from one or more electric components, an evaporator with evaporator channels, the evaporator being in thermal contact with a second surface of the base plate for transferring said heat load into a first fluid in the evaporator channels, a condenser (8, 8') with condenser channels (9, 9') having upper ends (33, 33') for receiving first fluid from upper ends (32, 32') of the evaporator channels and for dissipating heat from the first fluid in the condenser channels (9, 9'), and a collector space (16, 16') for receiving first fluid from the condenser (8, 8'), wherein the collector space (16, 16') is located higher than the lower ends (34, 34') of the evaporator channels and is in fluid communication with lower ends (34, 34') of the evaporator channels, wherein the first fluid received from the condenser (8, 8') to the collector space (16, 16') is passed to the lower ends (34, 34') of the evaporator channels in an operating state of the heat exchanger (1, 1'), and wherein the heat exchanger (1, 1') comprises a chamber in an upper part of the heat exchanger (1, 1') which is in fluid communication with the upper ends (32, 32') of the evaporator channels and with the upper ends (33, 33') of the condenser channels (9, 9') for passing the first fluid from the evaporator to the condenser (8, 8') characterized in that the evaporator is provided with tubes (36, 36') having internal longitudinal walls dividing the tubes (36, 36') into the evaporator channels, and wherein the evaporator comprises a plurality of said tubes (36, 36') stacked against each other along the second surface of the base plate to be parallel with each other such that the evaporator channels of the tubes (36, 36') extend parallel with each other. a base plate with a first surface for receiving a heat load from one or more electric components, an evaporator with evaporator channels, the evaporator being in thermal contact with a second surface of the base plate for transferring said heat load into a first fluid in the evaporator channels, a condenser (8, 8') with condenser channels (9, 9') having upper ends (33, 33') for receiving first fluid from upper ends (32, 32') of the evaporator channels and for dissipating heat from the first fluid in the condenser channels (9, 9'), and a collector space (16, 16') for receiving first fluid from the condenser (8, 8'), wherein the collector space (16, 16') is located higher than the lower ends (34, 34') of the evaporator channels and is in fluid communication with lower ends (34, 34') of the evaporator channels, wherein the first fluid received from the condenser (8, 8') to the collector space (16, 16') is passed to the lower ends (34, 34') of the evaporator channels in an operating state of the heat exchanger (1, 1'), and wherein the heat exchanger (1, 1') comprises a chamber in an upper part of the heat exchanger (1, 1') which is in fluid communication with the upper ends (32, 32') of the evaporator channels and with the upper ends (33, 33') of the condenser channels (9, 9') for passing the first fluid from the evaporator to the condenser (8, 8') characterized in that the evaporator is provided with tubes (36, 36') having internal longitudinal walls dividing the tubes (36, 36') into the evaporator channels, and wherein the evaporator comprises a plurality of said tubes (36, 36') stacked against each other along the second surface of the base plate to be parallel with each other such that the evaporator channels of the tubes (36, 36') extend parallel with each other.