A chip stack package is provided, wherein semiconductor chips having different die sizes are stacked by arranging pads in a scribe region through a redistribution process, so that the thickness of the package can be reduced. A method of fabricating the chip stack package is also provided. In the chip stack package, a plurality of circuit patterns are arranged on one surface of a substrate, and a unit semiconductor chip is mounted thereon. The unit semiconductor chip includes a plurality of semiconductor chips sequentially stacked on the substrate. The semiconductor chips of the unit semiconductor chip have different die sizes. One of the semiconductor chips includes a plurality of first pads arranged in a first chip region, and the other semiconductor chips include second pads arranged in a scribe region at an outside of a second chip region defined by the scribe region.