The continuing miniaturization and increasing power density of electronic and optoelectronic devices have made compact, lightweight, reliable heat dissipation challenging, particularly for boards with many discrete hotspots. Conventional finned heat sinks reject heat in an isotropic, undirected manner; therefore, much of the fin volume far from the active sources contributes little to convection but adds mass and occupies space. In this work, we embedded a thermal-shield metastructure into the fin field to convert a conventional sink into a heat-flux-routing device that concentrated conductive heat flow into prescribed regions, so fins were installed only where they are useful. Building on transformation-thermotics-inspired unit-cell thermal shifters formed by alternating high- and low-conductivity layers, we used the thermal-shield concept to prescribe a heat-routing fin layout, i.e., a metastructured (“meta-fin”) sink whose fins populate only the shield-defined region of a multi-hotspot module. Using transient three-dimensional finite-element heat-transfer simulations with prescribed convective boundary conditions, we compared it with pin- and plate-fin baseline sinks matched in surface area or volume and weight. The simulations showed that the meta-fin increased the surface-utilization efficiency by >10% relative to the full-footprint pin- and plate-fin baselines and exhibited 15%–25% higher transient heat rejection across the comparison set, while reducing material volume and mass by ~45% relative to the full-footprint baselines. Thus, its mass-normalized transient heat rejection was ~2× that of a conventional sink. It additionally enabled control of the on-chip temperature landscape, producing a diagonal temperature contrast more than 2.5× that of the conventional full-footprint designs. These improvements arise from redesigning the fin layout rather than introducing new functional materials. Moreover, rapid advances in additive manufacturing and 3D printing provide practical fabrication routes for such unconventional heat-sink form factors, supporting the future demonstration, refinement, and deployment of metastructure-based thermal management.