A detailed numerical simulation of forced convection heat transfer occurring in silicon-based microchannel heat sinks has been conducted using a simplified three-dimensional conjugate heat transfer model (2D fluid flow and 3D heat transfer). The micro-heat sink model consists of a 10 mm long silicon substrate, with rectangular microchannels, 57 mum wide and 180 mum deep, fabricated along the entire length. A finite difference numerical code with a Tri-Diagonal Matrix Algorithm (TDMA) was developed to solve the governing equations. The validated code provided detailed temperature and heat flux distributions in the microchannel heat sink. The influence of the geometric parameters of the channel and the thermophysical properties of the fluid on the flow and heat transfer, are investigated by evaluating thermophysical properties at a reference bulk temperature. The results indicate that thermophysical properties of the liquid can significantly influence both the flow and heat transfer in the microchannel heat sink. The bulk liquid temperature is shown to vary in a quasi-linear form along the flow direction for high fluid flow rates, but not for low flow rates. Comparison of the numerical results with other published numerical results and experimental data available in the literature for Reynolds numbers less than 200 based on a hydraulic diameter of D-h = 86 mum and D-h/L-x < 0.01, indicates that the assumption of hydrodynamic, fully developed laminar flow is valid. The thermal entrance length is also obtained from the detailed local heat transfer coefficient calculation and a correlation for the overall averaged Nusselt number is developed and discussed. Finally, a methodology is proposed whereby measured data can be evaluated and processed in order to provide a more complete understanding and better interpretation of these experimental data. (C) 2004 Elsevier Ltd. All rights reserved.