This brief presents a novel monolithic ultra-low leakage current sensor with large dynamic range. The sensor features an integrated digitizing circuit that generates digital output corresponding to changing leakage current levels, eliminating the need for an explicit ADC. Fabricated in a 180nm BCD process, the sensor occupies just 0.0234 mm 2 of area, consumes 3.1 mW of power and operates at 3.125MHz. It achieves a dynamic range of 25 pA to 5.5 µA, outperforming previous publications by several orders of magnitude. Measurement results demonstrate the sensor's accuracy, with INL and DNL remaining below 0.4 LSB across a temperature range of −40 • C to 125 • C. The sensor's ultra-low sensing capability and wide dynamic range make it suitable for time-dependent dielectric breakdown (TDDB) characterization and in-field reliability monitoring of circuits, enhancing reliability assessments in safety-critical systems.