Complementary metal-oxide-semiconductor (CMOS) image sensors are provided. A CMOS image sensor includes a substrate including a pixel array and a peripheral circuit region, a photodiode and a floating diffusion region in the pixel array of the substrate, a transfer gate insulating layer and a transfer gate electrode on the substrate between the photodiode and the floating diffusion region, and a peripheral gate insulating layer and a peripheral gate electrode on the peripheral circuit region. The transfer gate electrode includes a first edge that is rounded to have a first radius of curvature, and the peripheral gate electrode includes a second edge that is rounded to have a second radius of curvature smaller than the first radius of curvature.