The objective of the present study was to investigate the effect of the aspect ratio of rectangular channels on the cooling characteristics of paraffin slurry flow with a linear array of discrete heat sources. Four key experimental parameters were the aspect ratio of the rectangular channel, the mass fraction of paraffin slurry, the heat flux of simulated VLSI chips, and the channel Reynolds number. The influence of the aspect ratio of the rectangular channel on the local heat transfer coefficients for both water and paraffin slurry at a heat flux of 40 W cm(-2) was greater than at a low heat flux. The paraffin slurry with a mass fraction of 5% showed the most efficient cooling performance in a rectangular channel with an aspect ratio of 0.20 regardless of the heat flux and the channel Reynolds number.