When boiling occurs in a micro-channel, the growing bubbles could be confined They expand both upstream and downstream and cause flow instability in the form of flow fluctuations. The instability occurs frequently when the Bond number of the fluid in the micro-channel is less than unity. To reduce the flow instability, installation of an inlet orifice at the upstream or the micro-channel expanding at the downstream are found to be effective. A generalized instability model for micro-channels was established, which includes the effects of both inlet orifice and channel expansion. Experiments of evaporating water in 48 parallel micro-channels with 353 mu m hydraulic diameter were conducted, and the generalized instability criterion was validated. (C) 2010 Elsevier Ltd. All rights reserved.