A package structure includes a bottom plate, a semiconductor package, a top plate, a screw and an anti-loosening coating. The semiconductor package is disposed over the bottom plate. The top plate is disposed over the semiconductor package, and includes an internal thread in a screw hole of the top plate. The screw penetrates through the bottom plate, the semiconductor package and the top plate, and includes an external thread. The external thread of the screw is engaged to the internal thread of the top plate, and the anti-loosening coating is adhered between the external thread and the internal thread.