Oxide degradation and breakdown are studied using Substrate Hot Electron (SHE) and Fowler-Nordheim (FN) injection techniques. It is shown that the generation of electron traps during stress and breakdown are identical with both techniques and therefore SHE-injection can be used to study breakdown mechanisms at medium oxide fields that are not accessible with FN-injection. Breakdown is found to occur when a critical electron trap density is reached. In the high field range, it is shown that this critical trap density corresponds to a critical hole fluence, linking the models based on electron trap generation and on hole fluence together.