Provided is a complementary metal-oxide-semiconductor (CMOS) image sensor. The CMOS image sensor can include a substrate having a first device isolation layer defining and dividing a first active region and a second active region, a photodiode disposed in the substrate and can be configured to vertically overlap the first device isolation layer, a transfer gate electrode can be disposed in the first active region and can be configured to vertically overlap the photodiode, and a floating diffusion region can be in the first active region. The transfer gate electrode can be buried in the substrate.