The concern about thermal performance of microelectronics is on the increase due to recent over-heating induced failures which have led to product recalls. Removal of excess heat from microelectronic systems with the use of heat sinks could improve thermal efficiency of the system. This paper investigates the effect of change in heat sink geometry on thermal performance of aluminium and copper heat sinks in microelectronics. Numerical studies on thermal conduction through an electronic package comprising a heat sink, chip, and thermal interface material were carried out. The thickness of the heat sink base and the height of the heat sink fins were varied in the study. The minimum and maximum temperatures of aluminium and copper heat sinks in the two models were investigated using steady state thermal conduction analysis. Better heat dissipation occurred in thinner base thickness and extended fins height for both aluminium and copper heat sinks. Aluminium heat sink recorded the lowest minimum temperatures in both investigations and is recommended as optimal thermal management material for heat sink production.