Microfluidic cooling with microgaps with surface area enhancements such as pin fins can potentially achieve superior thermal performance in cooling high power microsystems. In this work, the single phase thermal/fluid characteristics of microgaps of H/W around 0.02, incorporating staggered pin fin arrays are studied. The effects of the pin fin dimensions including diameter, transversal and longitudinal spacing, and height are investigated by experimentally validated model over a range of Reynolds number (Re) 22-357. Micropin fin arrays investigated have pin diameter of 100 mu m, pitch/diameter ratios of 1.5-2.25, and height/diameter ratios of 1.5-2.25. Correlations of friction factor (f) and Colburn j factor for these dense arrays of micro pins have been developed. The performance of circular and square micro pin fin arrays were compared, showing that the circular array has better thermal performance under the same pumping power. (C) 2017 Published by Elsevier Ltd.