Example embodiments may provide a CMOS image sensor. The CMOS image sensor may include a plurality of unit blocks each including two unit pixels. Each unit block may include two photodiodes having a hexagonal shape, a floating diffusion shared by the two unit pixels, a first transfer transistor and a second transfer transistor between the floating diffusion and the two photodiodes, respectively, a reset transistor connected with the floating diffusion, a drive transistor with a gate connected with the floating diffusion, and/or a selection transistor connected to the drive transistor in series. Example embodiment CMOS image sensors may be used in digital cameras, mobile devices, computer cameras, or the like.