The rapid development of electronics, coupled with need of miniaturization in the design and manufacture, makes heat dissipation, which is critical for the performance, lifetime, and reliability of the components extremely challenging. To achieve higher heat dissipation rates, novel fin geometry with variable cross-section considering melting behaviour in medium is presented for PCM-based heat sink beyond previous efforts in literature. In this experimental study, effect of different variable cross-section, which refer different fin width ratio (s = 1, 0.5, 0.2 and 0) values are performed on the thermal performance of plate fin-based heat sink with PCM to enhance melting heat transfer. Decreasing fin width ratios point out increasing heat transfer surface area downwardly. N-eicosane is used. The constant input power is provided at the heat sink base. Thermal perfor-mance of novel fin design is evaluated by time-dependent temperature distributions, solid-liquid interface tracking photographs, reliable operating time, enhancement ratio, and thermal conductance. The results reveal that the proposed plate-fin geometry has a significant effect on the cooling performance of PCM-based heat sink. With the decrease of fin width ratio, higher temperature profile with more uniformity of 52% in the PCM me-dium, and so lower temperature distribution of 4.5% on the heat sink base are provided. Reliable operating time and thermal conductance values go up 15 % and 38%, respectively, for proposed fin geometry. The improvement on the thermal performance is achieved by the form of the plate-fin, which has increased surface area downward. This provides a great contribution to the conduction and convection heat transfer mechanisms at the lower half of the enclosure. Further, in this study, nearly the same reliable operating time is figured out with proposed fin geometry and fin number of s = 0 compared to higher fin number installation of s = 1 previously reported.