A semiconductor package and a manufacturing method thereof are provided. The semiconductor package includes at least one semiconductor die, an interposer, an encapsulant, a protection layer and connectors. The interposer has a first surface, a second surface opposite to the first surface and sidewalls connecting the first and second surfaces. The semiconductor die is disposed on the first surface of interposer and electrically connected with the interposer. The encapsulant is disposed over the interposer and laterally encapsulating the at least one semiconductor die. The connectors are disposed on the second surface of the interposer and electrically connected with the at least one semiconductor die through the interposer. The protection layer is disposed on the second surface of the interposer and surrounding the connectors. The sidewalls of the interposer include slanted sidewalls connected to the second surface, and the protection layer is in contact with the slant sidewalls of the interposer.