A CMOS active pixel sensor includes a photodiode, a transmitting transistor, a reset transistor, a fingered type source follower transistor and a selecting transistor, where the photodiode generates charge in response to incident light, the transmitting transistor transmits the charge stored in the photodiode to a sensing node, the reset transistor, coupled to a power supply voltage, resets a voltage of the sensing node so that the sensing node has substantially a level of the power supply voltage, the fingered type source follower transistor amplifies the voltage of the sensing node, the selecting transistor transmits a voltage of a source electrode of the fingered type source follower transistor into an internal circuit in response to a selection signal, thus, the channel width of the source follower transistor may be increased, and the MOS device noise due to the source follower transistor may be reduced.