The performance of a novel design of a three-section plate-fin heat sink employing channels of stepwise decreasing hydraulic diameter is numerically and experimentally evaluated. Prototype heat-sink and inlet outlet manifold configurations have been manufactured and characterized, in terms of thermal resistance and induced pressure drop, in a closed fluid loop experimental rig and for flow rates in the range of 20-40 mL/s. The flow development and particularly the secondary flow pattern inside the heat sink are investigated by means of a numerical three-dimensional model. The findings of the study establish that the induced pressure drop, which does not exceed 1000 Pa for the considered flow rates, is primarily attributed to the flow friction in the third-heat sink section, which is of microscale dimensions and the effect of the inlet outlet manifold system is very small (0.5% of the total). In terms of heat transfer, the effect of buoyancy in the first heat-sink section has a beneficial impact on thermal performance maintaining the thermal resistance constant, at a value approximately equal to 0.015 K/W, regardless of the flow rate of the cooling fluid. Heat transfer is also enhanced in the successive sections due to the effect of contraction-induced longitudinal vortices. Finally, it is proven that the heat sink wall exhibits a more uniform temperature distribution with the decrease of the Reynolds number. (C) 2014 Elsevier Ltd. All rights reserved.