This study focuses mainly on the prediction of saturated flow boiling heat transfer in microchannels. A wide range of experiments has been carried out with de-ionized water to obtain a comprehensive data set. Experiments of mass fluxes of 51-728.7kg/m(2)s, wall heat fluxes of 36-221.7kW/m(2), vapor qualities of 0.01-0.69, liquid Reynolds number of 7.72-190, aspect ratios of 0.37-5.00 (with a constant hydraulic diameter of 100 mu m) and hydraulic diameters of 100-250 mu m (for constant aspect ratio = 1). A new correlation including the aspect ratio effect is proposed to predict the heat transfer coefficient for saturated flow boiling in microchannels. The proposed correlation shows very good predictions with an overall mean absolute error of 16.9% and 86.4%, 96.2% and 99.5% of the predicted data falling within +/- 30, +/- 40 and +/- 50% error bands, respectively.