In　order　to　improve　the　thermal　characteristics　of　SOI　SiGe　HBT,　a　novel　structure　of　SiO2/Si3N4/SiO2　insulators　is　proposed,　considered　that　the　thermal　conductivity　of　Si3N4　is　much　higher　than　that　of　Sift,.　With　the　aid　of　the　thermal-electrical　model　of　SOI　SiGe　HST　with　SiO2/Si3N4/SiO2　insulators,　the　thermal　characteristics　of　the　device　is　studied.　The　thermal　resistance　(R-th),　thermal　time　constant　(tau),　and　thermal　capacity　(C-th)　are　adopt　to　represent　the　steady-state　and　transient　thermal　characteristics,　respectively.　It　is　shown　that　R-th,　tau,　and　C-th　of　the　novel　device　are　decreased　by　19.6%,　24.14%,　and　5.36%,　respectively,　when　compared　with　that　of　traditional　SOI　SiGe　HBT　with　SiO2　insulator.　In　addition,　for　the　novel　device,　the　improvement　of　R-th　and　tau　is　kept　with　the　increase　of　the　dissipated　power　from　2mW　to　12mW,　Furthermore,　for　the　novel　device,　the　influence　of　Si3N4　thickness　on　R-th　and　x　is　also　studied.　All　of　R-th,　tau,　and　C-th　are　decreased　with　the　increase　of　the　thickness　of　the　Si3N4　(tsoka).　Both　the　trend　of　R-th　and　tau　can　be　approximated　by　a　linear　function　with　t(Si3N4),　while　the　trend　of　C-th　can　be　approximated　by　an　exponential　function.　The　results　above　provides　a　guideline　to　the　improvement　of　the　thermal　characteristics　of　conventional　SOI　SiGe　HBTs,　making　the　device　more　suitable　for　high-temperature　applications.