In this work, the breakdown transients of A l 2 O 3- and HfO2-based metal-insulator-metal (MIM) stacks with the same oxide thickness and identical metal electrodes were compared. Their connection with the thermal properties of the materials was investigated using alternative experimental setups. The differences and similarities between these transients in the fast and progressive breakdown regimes were assessed. According to the obtained results, A l 2 O 3 exhibits longer breakdown transients than HfO2 and requires a higher voltage to initiate a very fast current runaway across the dielectric film. This distinctive behavior is ascribed to the higher thermal conductivity of A l 2 O 3. Overall results link the breakdown process to the thermal properties of the oxides under test rather than to dissipation effects occurring at the metal electrodes.