The off‐state leakage characteristics ofn‐channel metal‐oxide‐semiconductor field‐effect transistors with pure oxide, low‐partial pressure nitrided (LPN) oxide, re‐oxidized LPN, and nitrogen‐annealed LPN oxide as the gate insulator, were investigated over the temperature range 300–400 K. In the high‐field region (above 7 MV/cm), the gate‐induced drain leakage was found to be due to band‐to‐band tunneling for all samples. Low‐field conduction was determined to be due to a gate current which was many orders of magnitude higher than the Fowler–Nordheim current observed in capacitors on the same wafers. A trap‐assisted tunneling model was employed, using a trap energy of 0.7 eV determined from the activation data, in order to explain the low‐field gate current. The most likely cause of this enhanced conduction is oxide degradation in the gate‐to‐drain overlap region created during the source/drain implant.