In the present paper, closed-form correlations which allow for thermal optimization of microchantiels are suggested. Asymptotic solutions for velocity and temperature distributions for the high channel-aspect-ratios, high conductivity ratios, and low Reynolds numbers are presented using the averaging approach. From the asymptotic solutions, explicit correlations for the optimal channel width and the optimal fin thickness are proposed. (C) 2007 Elsevier Ltd. All rights reserved.