A package structure includes a metal sheet having perforations; a semiconductor chip having an active surface and an opposite inactive surface, wherein the active surface has electrode pads thereon, conductive bumps are disposed on the electrode pads, the semiconductor chip is combined with the metal sheet via the inactive surface thereof, a protective buffer layer is formed on the active surface to cover the conductive bumps, and the perforations are arranged around a periphery of the inactive surface of the semiconductor chip; an encapsulant formed on the metal sheet and in the perforations, for encapsulating the semiconductor chip and exposing the protective buffer layer; and a circuit fan-out layer formed on the encapsulant and the protective buffer layer and having conductive vias penetrating the protective buffer layer and electrically connecting to the conductive bumps. A method of fabricating the package structure and a package-on-package device including the package structure are also provided.