A semiconductor package structure including a first semiconductor package is provided. The first semiconductor package includes a first redistribution layer (RDL) structure having a first surface and a second surface opposite thereto. A first semiconductor die is disposed on and electrically coupled to the first surface of the first RDL structure. A first molding compound is disposed on the first surface of the first RDL structure and surrounds the first semiconductor die. A plurality of solder balls or conductive pillar structures is disposed in the first molding compound and electrically coupled to the first semiconductor die through the first RDL structure. A method for forming the semiconductor package is also provided.