A stack package includes a base substrate having connection pads on an upper surface thereof and ball lands on a lower surface thereof; at least two semiconductor chips stacked by intervening a spacer on the base substrate and defined with through-holes for electrical connections on positions corresponding to the connection pads; electrical connection members for electrically connecting the stacked semiconductor chips and the base substrate to each other; a pair of heat sinks formed such that they contact the side surfaces of the stacked semiconductor chips and extend in a direction perpendicular to the base substrate; and outside connection terminals attached to the ball lands located on the lower surface of the base substrate.