Provided is a semiconductor package including a lower package, an interposer on the lower package, and an upper package on the interposer. The lower package may include a lower package substrate, a lower semiconductor chip on the lower package substrate, and a lower heat-transfer layer on the lower semiconductor chip. The interposer may include an interposer substrate, first and second heat-transfer openings defined by recessed bottom and top surfaces, respectively, of the interposer substrate, an upper interposer heat-transfer pad disposed in the second heat-transfer opening, and an upper heat-transfer layer disposed on the upper interposer heat-transfer pad. The upper package may include an upper package substrate, an upper package heat-transfer pad, which may be disposed in a third heat-transfer opening defined by a recessed bottom surface of the upper package substrate, and an upper semiconductor chip disposed on the upper package substrate.