Based　on　traditional　transmission　line　method　(TLM),　an　improved　method　was　used　to　investigate　the　failure　mechanism　of　n-GaNlTilAl/NilAu　ohmic　contact　under　high-current　density　(＞10sA/cm2).　A　novel　structure　is　proposed　and　fabricated.　The　degradation　of　the　ohmic　contact　was　studied　by　the　novel　structure.　According　to　analyzing　the　energy　spectrum　of　the　sample　before　and　after　degradation,　it　is　concluded　that　Aluminium　diffusion　is　the　main　factor　that　destroyed　the　good　ohmic　contact.　©2009　IEEE.