Flow boiling in arrays of parallel microchannels is investigated using a silicon test piece with imbedded discrete heat sources and integrated local temperature sensors. The microchannels considered range in width from 102 mu m to 997 mu m, with the channel depth being nominally 400 mu m in each case. Each test piece has a footprint of 1.27 cm by 1.27 cm with parallel microchannels diced into one surface. Twenty five microsensors integrated into the microchannel heat sinks allow for accurate local temperature measurements over the entire test piece. The experiments are conducted with deionized water which enters the channels in a purely liquid state. Results are presented in terms of temperatures and pressure drop as a function of imposed heat flux. The experimental results allow a critical assessment of the applicability of existing models and correlations in predicting the heat transfer rates and pressure drops in microchannel arrays, and lead to the development of models for predicting the two-phase pressure drop and saturated boiling heat transfer coefficient. (C) 2007 Elsevier Ltd. All rights reserved.