A semiconductor package assembly is provided. The semiconductor package assembly includes a first semiconductor package. The first semiconductor package includes a first semiconductor die. A first redistribution layer (RDL) structure is coupled to the first semiconductor die and includes a first conductive trace. The semiconductor package assembly also includes a second semiconductor package bonded to the first semiconductor package. The second semiconductor package includes a second semiconductor die. An active surface of the second semiconductor die faces an active surface of the first semiconductor die. A second RDL structure is coupled to the second semiconductor die and includes a second conductive trace. The first conductive trace is in direct contact with the second conductive trace.