Present paper experimentally studies combined influence of artificial nucleation sites and expanding cross section on saturated flow boiling performance of heat sinks with micro pin fins. Thermal and visualization-based flow analysis is conducted. A novel micro pin fin heat sink having artificial nucleation sites and enlarging flow passages is designed; and compared with two different conventional heat sinks (parallel channel and uniform pin fin distribution) at different heating powers (from 90 W to 180 W or 132-272 kW m(-2) heat flux range), constant mass flux (approximately 287 kg m(-2) s(-1)) and inlet temperature (nearly 75 ?). Novel heat sink leads to improvement in heat transfer coefficient up to 557.8% against plain walled parallel channel heat sink, and up to 463.8% against uniformly distributed finned one. Compared to heat sink with uniform-distributed fins, a reduction in pressure drop up to 27.7% is achieved via the novel one. Liquid trapping phenomenon by artificial nucleation sites (ANSs), contribution of ANSs to nucleation, vacuum effect created by gradually increasing cross section, and effective prevention of bubble blockage are revealed to be basic underlying physical reasons of thermal and flow-based success.