The laminar flow characteristics inside slightly tapered silicon microchannels in the hydraulic diameter range of 53-112 mu m are investigated. Velocity profiles for planes located at different channel depth are measured using micro resolution particle image velocimetry (micro-PIV). It is revealed that the location of the maximum velocity deviates from the mid-plane along the depth direction due to the wall taper. Numerical simulations are also carried out to examine the effects of the sidewall angle on flow and heat transfer. Large deviation in the velocity profile and consequent significant degradation in heat transfer are observed for considerably tapered microchannels. (c) 2007 Elsevier Ltd. All rights reserved.