A hybrid cooling device for cooling the electronic cards by using dry and liquid cooling techniques under a single thermal management system, the hybrid cooling device comprising - an enclosure which has at least three separate sections, ▪ at least one spray/immersion section which is divided into two sections, being spray section and immersion section, and in which the liquid cooling process in the enclosure is realized, ▪ at least one dry cooling section which is isolated from the spray/immersion section and in which the dry cooling process is realized in the enclosure, - a plurality of slots which are provided inside the spray/immersion section and the dry cooling section and adapted to fix the electronic modules, - at least one reservoir provided inside the enclosure for storing the dielectric liquid therein, - at least one heat discharge section which is provided outside the spray/immersion section, in which the water in the reservoir is cooled via a heat exchanger and a fan, - at least one pump adapted to transfer the water in the reservoir to the heat discharge section for cooling, - at least one condenser which is connected to the outlet of the heat exchanger and adapted to convert the liquid vaporized in the spray/immersion section into liquid phase again, - at least two spray/immersion channels one of which is provided in the spray section, connected to the outlet of the one of the liquid channels and adapted to transfer the liquid in the liquid channels to the spray/immersion section, and the other one of which is provided in the immersion section, one end of which is connected to the outlet of the other liquid channel and the other end of which is adapted to open to the spray/immersion section of the liquid and which is adapted to fill the liquid in the liquid channels into the spray/immersion section, - at least one nozzle which is provided at the end of the spray/immersion channel in the spray section of the spray/immersion section, and adapted to atomize the liquid and then to spray the liquid onto the electronic components, and characterized by - at least two liquid channels which are adapted to pass on at least one of the sidewalls in the dry cooling section, through which the liquid passes for cooling the slots into which the electronic cards are attached, and which are adapted to transfer the said liquid to the spray/immersion liquids in the spray section and the immersion section. - an enclosure which has at least three separate sections, ▪ at least one spray/immersion section which is divided into two sections, being spray section and immersion section, and in which the liquid cooling process in the enclosure is realized, ▪ at least one dry cooling section which is isolated from the spray/immersion section and in which the dry cooling process is realized in the enclosure, ▪ at least one spray/immersion section which is divided into two sections, being spray section and immersion section, and in which the liquid cooling process in the enclosure is realized, ▪ at least one dry cooling section which is isolated from the spray/immersion section and in which the dry cooling process is realized in the enclosure, - a plurality of slots which are provided inside the spray/immersion section and the dry cooling section and adapted to fix the electronic modules, - at least one reservoir provided inside the enclosure for storing the dielectric liquid therein, - at least one heat discharge section which is provided outside the spray/immersion section, in which the water in the reservoir is cooled via a heat exchanger and a fan, - at least one pump adapted to transfer the water in the reservoir to the heat discharge section for cooling, - at least one condenser which is connected to the outlet of the heat exchanger and adapted to convert the liquid vaporized in the spray/immersion section into liquid phase again, - at least two spray/immersion channels one of which is provided in the spray section, connected to the outlet of the one of the liquid channels and adapted to transfer the liquid in the liquid channels to the spray/immersion section, and the other one of which is provided in the immersion section, one end of which is connected to the outlet of the other liquid channel and the other end of which is adapted to open to the spray/immersion section of the liquid and which is adapted to fill the liquid in the liquid channels into the spray/immersion section, - at least one nozzle which is provided at the end of the spray/immersion channel in the spray section of the spray/immersion section, and adapted to atomize the liquid and then to spray the liquid onto the electronic components, and characterized by - at least two liquid channels which are adapted to pass on at least one of the sidewalls in the dry cooling section, through which the liquid passes for cooling the slots into which the electronic cards are attached, and which are adapted to transfer the said liquid to the spray/immersion liquids in the spray section and the immersion section.