This invention provides an image sensor module with a three-dimensional die-stacking structure. By filling a conductive material into through silicon vias within at least one image sensor die, and into via holes within an insulating layer, vertical electrical connections are formed between the image sensor die and an image processor buried in the insulating layer. A plurality of solder bumps is formed on a backside of the image sensor module so that the module can be directly assembled onto a circuit board. The image sensor module of this invention is characterized by a wafer-level packaging architecture and a three-dimensional die-stacking structure, which reduces electrical connection lengths within the module and thus reduces an area and height of the whole packaged module.