A semiconductor package structure is provided. The structure includes a first semiconductor die having a first surface and a second surface opposite thereto. A first molding compound surrounds the first semiconductor die. A first redistribution layer (RDL) structure is disposed on the second surface of the first semiconductor die and laterally extends on the first molding compound. A second semiconductor die is disposed on the first RDL structure and has a first surface and a second surface opposite thereto. A second molding compound surrounds the second semiconductor die. A first protective layer covers a sidewall of the first RDL structure and a sidewall of the first molding compound.