Provided is a CMOS image sensor with an asymmetric well structure of a source follower. The CMOS image sensor includes: a well disposed in an active region of a substrate; a drive transistor having one terminal connected to a power voltage and a first gate electrode disposed to cross the well; and a select transistor having a drain-source junction between another terminal of the drive transistor and an output node, and a second gate electrode disposed in parallel to the drive transistor. A drain region of the drive transistor and a source region of the select transistor are asymmetrically arranged.