Combined effects of fin number and inclination angle on the thermal performance of a PCM-based heat sink with longitudinal plate fins are investigated experimentally. Five different heat sink geometries with one, two, three, four and five fins are tested under different inclination angles varied from 0 degrees to 90 degrees at a constant thermal load of 16 W for the cases of with and without PCM inclusion. N-eicosane is used as the phase change material. Simultaneous temperature measurements and solid-liquid interface imaging are made to evaluate cooling performance of each heat sink configuration. The results reveal that the inclination angle and fin number plays a critical role on the formation of convective cells in the liquid PCM domain and consequently on the heat transfer and operating time. It is disclosed that the heat sink configuration with an inclination angle of 60 degrees and three fins performs the optimal result in terms of operating time.