Radiation sensor interface circuits can be mounted on sensor nodes in wireless sensor networks to detect radiation signals. They respond quickly to operators and command centers, allowing appropriate decisions to be made to mitigate nuclear power plant accidents. For instance, high-level radiation leaked from a reactor building during a nuclear plant accident can degrade the performance of the radiation sensor interface implemented by integrated circuits due to threshold voltage shift, leakage current change, and noise increase induced by radiation impact events. To obtain reliable signal measurements in the high radiation environment, radiation-hardening technologies must be applied to radiation sensor interface circuits. The radiation-hardened sensor interface circuit proposed in this article exploits a pair of charge-sensitive amplifiers (CSAs) in dual paths to equivalently cancel out the distorted output signals caused by radiation impacts on the circuits. In addition, a low-power, fully differential successive approximation register (SAR) analog-to-digital converter (ADC) is used to reduce the radiation effects by subtracting the radiation-induced noise of one input from the other. The implemented radiation sensor interface circuit can maintain its performance up to 1.0 mrad (SiO2) of irradiation with only 2.5 mW power consumption, while successfully sensing and transferring the radiation information to the downstream signal-processing network.