Computational experiments were performed to study the influence of microchannel width and aspect ratio on performance of a four-compartment, microchannel heat sink with dedicated coolant inlet and outlet for each compartment. Wide range of coolant velocity (0.25-2 m/s) & aspect ratio (2-10) and a reasonable range of microchannel width (100-200 mu m) have been simulated. The appropriate microchannel width and aspect ratio were found to be 200 mu m and 6, as evidenced from lowest total thermal resistance and lowest non-uniformity of substrate temperature at comparable power consumption among different microchannel widths and aspect ratios simulated. A new parameter 'omega' has been proposed for representation of substrate temperature gradient considering maximum, average and minimum substrate temperatures. Correlations have been developed for prediction of dimensionless pumping power, Nusselt number and dimensionless total thermal resistance. Hence, the four compartment heat sink with 200 mu m wide channels of aspect ratio 6 can be used for energy-efficient thermal management. (C) 2015 Elsevier Ltd. All rights reserved.