Abstract: A new photodetector, the bipolar junction photogate transistor, was proposed for CMOS image sensor. The transient model of the bipolar junction photogate transistor was built.The photo-current characteristics of the bipolar junction photogate transistor are obtained under the 0.6μm CMOSprocess parameter by applying the multiple-transient methods of the HSPICE software.Due to an injection p⁺n junction introduced, the readout rate of the photo-charges increases. The simulatingresults show that the photocurrent increases following the exterior voltage according to the exponent way and the blue respond characteristic is rather improved.