The inventive concepts provide package-on-package (PoP) devices. In the PoP devices, an interposer substrate and a thermal boundary material layer may be disposed between a lower semiconductor package and an upper semiconductor package to rapidly exhaust heat generated from a lower semiconductor chip included in the lower semiconductor package. The interposer substrate may be formed of one or more insulating layers, conductive vias, heat dissipating members, protection layers, and various conductive patterns.