For applications of high-power LED illumination and advanced CPU electronic cooling, since the traditional plate heat sinks by aluminum extrusion are simple geometry only and with limited thermal performance, a new design and new fabrication process of heat sink for high-density heat flux applications is inevitable. In this study, a heat sink fabricated by vacuum die-casting is analyzed. To evaluate the thermal performance of this heat sink, two experiments, free convection measurements in an enclosure and forced convection measurements in a wind tunnel, are conducted by two experimental methods of thermocouples and IR thermograph. As to free convection experiments, compared to the free convection over a plate, temperature decrement by the attached casting of pin-fin heat sink is 46.2% for the input power of 10W. In the case of 15W heating power, temperature distribution along center pin shows uniformly distributed temperature along length direction, but there is a temperature difference of 9.5°C,varied from 86.9°C to 77.4°C, at outer pin. As to the case of 10W heating power, there is a temperature difference of 6.5°C, varied from 69.2.9°C to 62.6°C, at the outer pin. Furthermore, forced convection experiments show that resistances of heat-sink casting are decreased when Reynolds numbers are increased, and a linear relationship between pressure drop and Reynolds number is noticed. Base on the measurement results, this heat sink casting can be a feasible thermal solution of LED and high-power chip products.