This work reports the effects of drain impact ionization injection on the gate dielectric breakdown. Results show that due to the high energy hot carrier injection, the gate oxide can break down twice at a low oxide electric field (< 1.2 MV/cm). The first breakdown occurs simultaneously with the drain avalanche breakdown whereas the second breakdown occurs beyond the drain breakdown. It is further identified that the first gate oxide breakdown is governed by the thermionic emission of hot electrons at low oxide fields (< 1.0 MV/cm) and by the scattering processes at higher oxide fields. The second breakdown is attributed to the Fowler-Nordheim (F-N) tunneling.