A sensor semiconductor device and a method for fabricating the same are proposed. A plurality of metal bumps and a sensor chip are mounted on a substrate. A dielectric layer and a circuit layer are formed on the substrate, wherein the circuit layer is electrically connected to the metal bumps and the sensor chip. Thus, the sensor chip is electrically connected to the substrate via the circuit layer and the metal bumps. The dielectric layer is formed with an opening for exposing a sensor region of the sensor chip. A light-penetrable lid covers the opening of the dielectric layer, such that light is able to penetrate the light-penetrable lid to reach the sensor region and activate the sensor chip. A plurality of solder balls are mounted on a surface of the substrate free of mounting the sensor chip, for electrically connecting the sensor chip to an external device.