The influence of channel length on total ionizing dose effect in a 180 nm complementary metal-oxide semiconductor technology is studied. When other conditions such as radiation bias, device structure are the same, the overall radiation response is determined by the charges trapped in the oxide. The off-state leakage due to the charges trapped in the shallow trench isolation oxide inverting the parasitic sidewall channel has correlation with the channel length. A shorter channel leads to a larger leakage current. For the first time, we report that the leakage current also exhibits the radiation enhanced channel-length modulation effect, which further degrades the device performance.