A unit pixel of a complementary metal-oxide semiconductor (CMOS) image sensor includes a photoelectric conversion element, a transfer transistor, a boosting capacitor and a signal transfer circuit, where the photoelectric conversion element generates a charge based on incident light, the transfer transistor transfers the charge to a floating diffusion node in response to a transfer control signal, the boosting capacitor is disposed between a gate of the transfer transistor and the floating diffusion node, the signal transfer circuit transfers an electric potential of the floating diffusion node in response to a selection signal, and a dynamic range of the electric potential of the floating diffusion node may be widened and a drain-source voltage difference of the transfer transistor may be increased so that the charge transfer efficiency may be enhanced.