Over-molded IC package assemblies including an embedded voltage reference plane and/or heat spreader. In some embodiments, an over-molded package assembly includes a IC chip or die coupled to one or more metal distribution layer or package substrate. A molding compound encapsulates at least the IC chip and one or more conductive layers are embedded within the molding compound. The conductive layers may include an interior portion located over the IC chip and a peripheral portion located over the redistribution layers or package substrate. The interior portion may comprise one or more heat conductive features, which may physically contact a surface of the IC chip. In some further embodiments, the peripheral portion comprises one or more electrically conductive features, which may physically contact a surface of the package redistribution layers or package substrate to convey a reference voltage. One or more conductive traces may connect the conductive features in the interior with conductive features in the periphery.