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