This study presents the numerical simulation of the heat sink with all un-uniform fill height with a confined impingement cooling. The governing equations are discretized by using a control-volume-based finite-difference method with a power-law scheme oil ail orthogonal non-uniform staggered grid. The coupling of the velocity and the pressure terms of momentum equations are solved by the SIMPLEC algorithm. The well-known k-epsilon two-equations turbulence model is employed to describe the turbulent structure and behavior. The parameters include the Reynolds number (Re = 15,000 and Re = 25,000) and 12 un-uniform fill height designs (Type-b to Type-m). The objective of this study is to examine the effects of the fill shape of the heat sink oil the thermal performance. It is found that the junction temperature call be reduced by increasing the fill height near the center of the heat sink. The results also show that there is a potential for optimizing the un-uniform fill height design. (c) 2008 Elsevier Ltd. All rights reserved.