Ultraviolet/blue photodetector based on UMC 0.18μm CMOS technology is proposed, which is constructed by a lateral/vertical PN diode and an NMOS transistor. The shallow PN diode formed by the Twell layer and Nwell layer is used to enhanced the absorption efficiency of Ultraviolet/blue light and separate the photogenerated carriers. Since the gate of NMOS is tied with the Twell layer, it can be adjusted by the Twell voltage induced by the incident illumination. The sensitivity and the dynamic range of the proposed detector are improved. The simulation results show that the detector has extra high responsivity and wide dynamic range for the wavelength window of 300~550 nm. Under the condition of weak light (<1 μW/cm2), the detector has a responsivity more than 105 A/W. With the increase of light intensity, the responsivity decreases but it still better than 103 A/W in the interesting range.