This paper describes the total ionizing dose effect on 0.18 μm narrow-channel NMOS transistors which are exposed to a γ-ray radiation. Electrical parameters such as threshold voltage, leakage current, trans-conductance, drain-source conductance, and subthreshold slope extracted from the I-V curves are analyzed pre-and post-irradiation. Results show that the threshold voltage, the trans-conductance, and the drain-source conductance are sensitive to radiation compared to wide-channel NMOS transistors–the effect we call radiation induced narrow channel effect(RINCE). The amount of oxide-trapped charges and interface states which would degrade the threshold voltage and leakage current is induced in the STI oxide. The gate oxide is insensitive to irradiation. Combining the structure and process of devices, we finally discuss and analyze the above phenomenon in detail.