Tremendous attentions have been focused on thermal management to control the temperature of many advanced integrated electronic devices. The liquid metal cooling has recently been validated as a highly effective method to dissipate heat from hot chips. In this study, a practical design and implementation of a buoyancy effect driven liquid metal cooling device for the automatic thermal management of hot chips in a closed cabinet were demonstrated. The principles, especially the theory for convective thermal resistance of liquid metal cooling was provided for guiding optimization of the device. A model prototype was then fabricated and tested. Experiments were performed when two simulated hot chips in the closed cabinet worked at different heat loads and different angles with the horizontal plane. It was shown that for the one chip case, the cooling device could maintain the chip temperature to below 85.1 °C at the ambient temperature 20 °C when the heat load was about 122 W. The cooling performance of the device could achieve better when the angle between the cabinet and the horizontal plane varied from 0 °C to 90 °C. With two chips working simultaneously, both chips had close temperature and hot spot did not appear easily when subject to large power, which will help reduce thermal stress and enhance reliability of the system. The practical value of the self-driven liquid metal cooling device is rather evident. Given its reliability, simplicity, and efficiency, such device can possibly be used for heat dissipation of multichip in closed space in the future.