Flow boiling of water across a bank of circular staggered micro-pin fins, 250 pm long and 100 mu m diameter with pitch-to-diameter ratio of 1.5, was experimentally studied for mass fluxes ranging from 346 kg/m(2) s to 794 kg/m(2) s and surface heat fluxes ranging from 20 W/cm(2) to 350 W/cm(2). Local temperature measurements were used to elucidate the two-phase heat transfer coefficients. The flow was visualized and classified as vapor slug and annular flow patterns. A flow map was constructed and compared with maps for adiabatic micro-scale systems and good agreement was observed. A superposition model for the two-phase heat transfer coefficient in convective boiling regime was developed. Frictional multiplier, ((phi(1))(2)), from micro-scale studies was used to define the enhancement factor (F) in the heat transfer coefficient model and reasonable agreement was obtained between experiments and predictions. (C) 2007 Elsevier Ltd. All rights reserved.