A method includes forming a plurality of first conductive vias over a redistribution layer (RDL); disposing a first die over the RDL and adjacent to the first vias; and forming a plurality of second conductive vias over and electrically connected to the first conductive vias, each of the second conductive vias corresponding to one of the first conductive vias. The method further includes forming a plurality of third conductive vias over the first die; disposing a second die over the first die and adjacent to the third conductive vias; and encapsulating the first die, the second die, the first conductive vias, the second conductive vias and the third conductive vias with a molding material.