A semiconductor package includes an interconnect structure including a redistribution structure, an insulating layer over the redistribution structure, and conductive pillars on the insulating layer, wherein the conductive pillars are connected to the redistribution structure, wherein the interconnect structure is free of active devices, a routing substrate including a routing layer over a core substrate, wherein the interconnect structure is bonded to the routing substrate by solder joints, wherein each of the solder joints bonds a conductive pillar of the conductive pillars to the routing layer, an underfill surrounding the conductive pillars and the solder joints, and a semiconductor device including a semiconductor die connected to a routing structure, wherein the routing structure is bonded to an opposite side of the interconnect structure as the routing substrate.