This invention provides a cooling system comprising a thermosyphon for computer and electronic devices. The thermosyphon comprises an evaporator placed on top of a heat source, such as CPU. Heat from the heat source causes liquid coolant inside the evaporator to evaporate or boil. The resulting vapor enters a condenser and returns to a liquid phase. Cooling fins are attached to the condenser to facilitate heat transfer with the surrounding airflow. The cooling system and computer or electronic device fit within standard computer cases and high density server rack-mountable cases.