A fully integrated sensor microsystem for blue/ultraviolet (UV) radiation detection is presented. The photosensitive part includes a 1-mm 2 blue/UV-selective stripe-shaped photodiode, which has maximal response in the short-wavelength range. A 15-times smaller infrared (IR) photodiode is added to compensate the parasitic photocurrent generated by the blue/UV photodiode in the IR range. Thus, a very high ratio of the responsivities at 420 nm and 1 μm of 1500 is achieved. A transimpedance amplifier with 1 GΩ feedback resistor followed by an inverter is integrated on the same silicon chip. The main features of the operational amplifier (op amp) are a low offset (<0.5 mV) and fail-safe operation. This sensor has a maximal responsivity of 150 mV/nW at λ=420 nm, corresponding to 44% quantum efficiency. The system has a noise equivalent power of 5×10 −13 W. The 2.2 mm 2 microsystem is realized in a standard CMOS 0.5 μm process without any post-processing step.