The shape optimization of the plate-fin type heat sink with an air deflector is numerically performed to minimize the pressure loss subjected to the desired maximum temperature and geometrical constraints. A function evaluation using the FVM, in general, is required much computational costs in fluid/thermal systems. Thus, global approximate optimization techniques have been introduced into the optimization of fluid/thermal systems. In this study, the Kriging method, which is one of the metamodels, associated with the computational fluid dynamics (CFD) is used to obtain the optimal solutions. The Kriging method can dramatically reduce a computational cost by 1/6 times compared to that of the SQP method so that its efficiency can be validated. The results also show that when the temperature rise is less than 40 K, the optimal design variables are B-1 = 2.44 mm, B-2 = 2.09 mm, and t = 7.58 mm. (c) 2006 Elsevier Ltd. All rights reserved.