A new type of fan-shaped cavity and trapezoidal rib microchannel heat sink is proposed. The performance of single cavity or rib and composite structures were compared by the univariate method in terms of velocity, pressure drop, and temperature. Based on enhanced heat transfer factor and entropy minimization method, the overall evaluation of micro radiators with different structures was carried out. The results show that the combined use of cavity and rib makes the boundary layer periodically interrupted and re-developed, and the combined heat dissipation effect of cavity and rib is better than that of a single rib or cavity structure. When Re is 1 300, the enhanced heat transfer factor is 1.535 4, much higher than 1.355 for a trapezoidal rib and 1.28 for a fan-shaped cavity. Entropy generation analysis shows that the combined structure has the least irreversible loss, which is consistent with the enhanced heat transfer factor.