A semiconductor package having a stiffening structure is disclosed. The semiconductor package includes a substrate, an interposer on the substrate, and a first logic chip, a second logic chip, memory stacks and stiffening chips, all of which are on the interposer. The first logic chip and the second logic chip are adjacent to each other. Each memory stack is adjacent to a corresponding one of the first logic chip and the second logic chip. Each memory stack includes a plurality of stacked memory chips. Each stiffening chip is disposed between corresponding ones of the memory stacks, to be aligned and overlap with a boundary area between the first logic chip and the second logic chip.