A method of fabricating a package-on-package (PoP) type of semiconductor package may include providing a lower package with a lower substrate, a lower semiconductor chip, and a lower mold layer and providing an upper package with an upper substrate, an upper semiconductor chip, and an upper mold layer. A through hole is formed to penetrate the upper package, and the upper package and lower package are electrically connected. A thermal interface material is injected into the through hole to form a first heat transmission part between, and in contact with, the upper package and the lower package.