The present invention provides a semiconductor structure for forming a CMOS image sensor. The semiconductor structure includes at least a photodiode formed in the substrate for collecting photoelectrons, and the photodiode has a pinning layer, a first doped region and a second doped region in order from top to bottom in a height direction of the substrate. The semiconductor structure further includes a third doped region located in the substrate corresponding to a laterally extending region of the second doped region. The first doped region has an ion doping concentration greater than the ion doping concentration of the second doped region, the ion doping concentration of the second doped region is greater than the ion doping concentration of the third doped region, and the third doped region is in contact with the second doped region after diffusion. The present invention also provides a method of manufacturing the above-described semiconductor structure.