The continuous scaling of semiconductor devices in AI HBM and IoT systems has made thermal management a critical challenge. Although epoxy composites are standard for packaging, neat epoxy’s low thermal conductivity (~0.2 W/m·K) necessitates conductive fillers. Conventional ceramic fillers like Al2O3 and SiO2 often yield composites below 1 W/m·K despite their high intrinsic values. To enhance thermal pathways while maintaining insulation, we introduced a hybrid filler system combining single-size Al2O3, multi-sized Al2O3, and MWCNTs to optimize packing efficiency. The microstructural morphology was examined via SEM, and thermal conductivity was measured using laser flash analysis. This hybrid approach demonstrated significant improvements over conventional filler configurations, offering a robust solution for high-density semiconductor packaging.