This study focuses on experimental evaluation of melting process in a horizontal heat sink for different configurations of plate fins. Paraffin RT35 with melting temperature of 29-35 degrees C is used as phase change material (PCM), while fins are made of copper. To simulate the use of heat sink in electronics cooling, the bottom side is subjected to 5W power supply. The trend of melting process, temperature distribution and the temperature variation of the heat sink base plate are studied for different fins numbers, fins heights and fins thicknesses. Visualization of the melting process provides the possibility of calculating the PCM melt fraction based on the conversion of color photos to black and white ones. Also the temperature distribution inside the enclosure is demonstrated using the temperature recording at the mid plane of the heat sink. Introduction of fins into the enclosure, results in higher melting rate and lower base temperature. Results indicate that by increasing the number of fins a more uniform temperature distribution is provided which improves the melting process more than other parameters. Moreover, results are also analyzed for two critical temperatures of 40 degrees C and 50 degrees C. It is revealed that when the critical temperature is lower, the number of fins is more effective on the temperature control of the heat sink base plate. Finally, results are generalized for PCM melt fraction and base temperature and the correlations are suggested based on a nonlinear regression analysis. (C) 2019 Elsevier Ltd. All rights reserved.