Abstract. This paper presents a numerical investigation in which thermal performance characteristics of pin fin heat sinks enhanced with phase-change materials (PCMs) designed for cooling of electronic devices are studied. The paraffin RT44 HC is poured into the aluminum pin fin heat sink container, which is chosen for its high thermal conductivity. The effects of different geometrical parameters, including number, thickness and height of fins, on performance are analyzed. Different aspects for heat transfer calculation, including the volume expansion in phase transition as well as natural convection in a fluid zone, are considered in the study. In order to validate the numerical model, previous experimental data and the present results are compared, and an acceptable agreement between these two is observed. Results show that increasing the number, thickness and height of fins leads to a significant decrease in the base temperature as well as operating time of the heat sink.