An active solid heatsink device and fabricating method thereof is related to a high-effective solid cooling device, where heat generated by a heat source with a small area and a high heat-generating density diffuses to a whole substrate using a heat conduction characteristic of hot electrons of a thermionic (TI) structure, and the thermionic (TI) structure and a thermo-electric (TE) structure share the substrate where the heat diffuses to. Further, the shared substrate serves as a cold end of the TE structure, and the heat diffusing to the shared substrate is pumped to another substrate of the TE structure serving as a hot end of the TE structure.