A semiconductor package assembly includes a first semiconductor package. The first semiconductor package has a semiconductor die having pads thereon, first vias disposed on the first semiconductor die, the first vias coupled to the pads. A second semiconductor package is stacked on the first semiconductor package and includes a body having a die-attach surface and a bump-attach surface opposite to the die-attach surface, a first memory die mounted on the bump-attach surface, coupled to the body, and a second memory die mounted on the die-attach surface, coupled to the body through the bonding wires. The number of input/output (I/O) pins of first memory die is different from the number of input/output (I/O) pins of the second memory die.