As a result of the development of micro-electro-mechanical systems (MEMS), it is now feasible to achieve enormous heat transfer, even though electrical and electronic devices have more compact spaces. A heat sink is a device that collects significant amounts of heat from various electrical and electronic surfaces and then releases that heat into the surrounding environment. In the current study, a ceramic microchannel heat sink (MCHS) with a rectangular channel having a length of 10 mm and dimensions of 57×180 μm was investigated numerically. Because ceramics are valuable materials that can withstand corrosive environments and extreme temperatures, they are statistically analyzed to evaluate whether a substance can work under such harsh conditions. Firstly, the finite element approach was used to solve the governing equations of the solid domain as ZrB2 composites and the fluid domain as water. Subsequently, a numerical analysis was conducted on an MCHS constructed from ZrB2 composites reinforced with SiC and CNT in a variable proportion of 20 vol.% and 10 vol.%, respectively. The results reveal the most significant temperature reduction for an ultra-high heat flux for the ZrB2 composite reinforced with 20 vol.% SiC, followed by the ZrB2 composite reinforced with 20 vol.% SiC & 10 vol.% CNT at Reynolds number 250. The fundamental causes of the exceptional heat transfer rate are the high surface density of the microchannel and the excellent thermal conductivity of the UHTCs.