The　study　presented　in　this　paper　contributes　to　the　quantification　of　the　correlations　between　resistance　degradation　and　Al　metallization　layer　reconstruction　observed　in　high-power　insulated　gate　bipolar　transistor　(IGBT)　modules　during　power　cycling.　The　microstructure　evolution　that　occurs　in　the　Al　metallization　layer　during　power　cycling　was　investigated　via　electron　and　ion　microscopy,　and　the　surface　roughness　was　measured　and　used　to　characterize　Al　metallization　degradation.　An　electrical　four-point　probe　method　was　used　to　examine　the　change　in　the　electrical　parameter　(resistance)　of　the　Al　metallization　layer　in　the　IGBT　modules.　The　effect　of　the　Al　metallization　layer　reconstruction　on　its　electrical　performance　was　investigated　by　experimental　observation　and　finite-element　analysis　(FEA).　The　results　show　that　both　the　Al　metallization　layer　surface　morphology　and　cracks　propagating　across　the　Al　metallization　layer　thickness　significantly　affect　the　metallization　resistance.　In　the　initial　and　midpoint　stages　of　power　cycling,　the　increase　in　the　Al　metallization　layer　resistance　is　consistent　with　the　surface　roughness　evolution.　Near　the　ultimate　lifetime　of　the　IGBT　module,　the　change　in　the　resistance　strongly　depends　on　the　crack　density.