An integrated fan-out (InFO) package includes a plurality of dies, an encapsulant, an insulating layer, a redistribution structure, a plurality of conductive structures, an antenna confinement structure, and a slot antenna. The encapsulant laterally encapsulates the dies. The insulating layer is disposed over the dies and the encapsulant. The redistribution structure is sandwiched between the insulating layer and the dies. The conductive structures and the antenna confinement structure are embedded in the insulating layer. The slot antenna is disposed on the insulating layer.