A stack package structure is provided, including: a substrate; an insulating layer formed on the substrate and having openings for exposing die attach pads and conductive pads of the substrate, respectively; a plurality of first and second conductive terminals formed on the insulating layer and electrically connected to the die attach pads and the conductive pads, respectively; a dielectric layer formed on the insulating layer and having a cavity for exposing the first conductive terminals and a plurality of openings exposing the second conductive terminals; copper pillars formed respectively in the openings of the dielectric layer; a semiconductor chip disposed in the cavity and electrically connected to the first conductive terminals; solder balls formed respectively on the copper pillars that are located proximate to the die attach area; and a package structure disposed on and electrically connected to the solder balls.