Package on package structure and fabrication method thereof

A method for fabricating a POP structure is disclosed. First, a first package is provided, which has: a dielectric layer; a stacked circuit layer embedded in the dielectric layer and exposed from upper and lower surfaces of the dielectric layer; a plurality of conductive posts and a semiconductor chip disposed on the upper surface of the dielectric layer and electrically connected to the stacked circuit layer; and an encapsulant formed on upper surface of the dielectric layer for encapsulating the semiconductor chip and the conductive posts and having a plurality of openings for exposing top ends of the conductive posts. Then, a second package is disposed on the encapsulant and electrically connected to the conductive posts. The formation of the conductive posts facilitates to reduce the depth of the openings of the encapsulant, thereby reducing the fabrication time and increasing the production efficiency and yield.