This work describes an experimental investigation of bubble dynamics and the effect on flow boiling instabilities and heat transfer in a multiple-microchannel heat sink. In this paper, results of the experimental investigation of bubble dynamics are presented and discussed. The microchannel heat sink contained 40 parallel, rectangular channels having hydraulic diameter of 194 mu m, and an aspect ratio of 0.549. The experiments were conducted with deionised water over a mass flux range from 71 to 204 kg/m(2) s, and an inlet temperature of 71 degrees C. Bubble growth rate and departure diameter under sub-cooled and saturated flow boiling are studied using a microscope and a high speed camera. The effects of mass flux and heat flux on bubbles growth characteristics are investigated and discussed. The results of this study demonstrate that the bubble growth rate in microchannels is different from that in macroscale channels. Confinement of microchannel and interaction between channels result in the unique bubble dynamic in microchannels. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.