A topology-optimized structure for thermal management is developed. The topology optimization is performed based on the minimization of objective functions under natural convection in two-dimensional space. The Boussinesq approximation is included in the momentum equation to simulate natural convection. A RAMP-style function is applied to the thermal conductivity in the design domain so as to clearly define the solid and liquid regions. The solid region represents AlSi10Mg, a high thermal conductivity aluminum alloy that is used for additive manufacturing, while the liquid region represents the phase change material (PCM). The optimization was computed with COMSOL Multiphysics. The structure is successfully fabricated by Selective Laser Melting (SLM) using AlSi10Mg powder. Experimental investigations of this structure were performed together with two conventional designs fabricated with Al-6061; one with five longitudinal fins positioned radially from the heat source and the other with no surface enhancements. The PCM used in the experiments is RT44HC. The experiments involved allowing the PCM to completely melt at two heat rates of 27 and 48 W. All structures were placed in the horizontal orientation. Our preliminary experimental studies suggest that the topology-optimized structure has a lower rate of increase in base temperature during post-melting compared to the two conventional designs, primarily due to the efficient transfer of heat by natural convection.