The　product　of　the　cutoff　frequency　and　breakdown　voltage　(f(T)　x　BVCEO)　is　an　important　figure　of　merit　(FOM)　to　characterize　overall　performance　of　heterojunction　bipolar　transistor　(HBT).　In　this　paper,　an　approach　to　introducing　a　thin　N+-buried　layer　into　N　collector　region　in　silicon-on-insulator　(SOI)　SiGe　HBT　to　simultaneously　improve　the　FOM　of　f(T)　x　BVCEO　and　thermal　stability　is　presented　by　using　two-dimensional　(2D)　numerical　simulation　through　SILVACO　device　simulator.　Firstly,　in　order　to　show　some　disadvantages　of　the　introduction　of　SOI　structure,　the　effects　of　SOI　insulation　layer　thickness　(T-BOX)　on　f(T),　BVCEO,　and　the　FOM　of　f(T)　x　BVCEO　are　presented.　The　introduction　of　SOI　structure　remarkably　reduces　the　electron　concentration　in　collector　region　near　SOI　substrate　insulation　layer,　obviously　reduces　f(T),　slightly　increases　BVCEO　to　some　extent,　but　ultimately　degrades　the　FOM　of　f(T)　x　BVCEO.　Although　the　fT,　BVCEO,　and　the　FOM　of　f(T)　x　BVCEO　can　be　improved　by　increasing　SOI　insulator　SiO2　layer　thickness　TBOX　in　SOI　structure,　the　device　temperature　and　collector　current　are　increased　due　to　lower　thermal　conductivity　of　SiO2　layer,　as　a　result,　the　self-heating　effect　of　the　device　is　enhanced,　and　the　thermal　stability　of　the　device　is　degraded.　Secondly,　in　order　to　alleviate　the　foregoing　problem　of　low　electron　concentration　in　collector　region　near　SOI　insulation　layer　and　the　thermal　stability　resulting　from　thick　TBOX,　a　thin　N+-buried　layer　is　introduced　into　collector　region　to　not　only　improve　the　FOM　of　f(T)　x　BVCEO,　but　also　weaken　the　self-heating　effect　of　the　device,　thus　improving　the　thermal　stability　of　the　device.　Furthermore,　the　effect　of　the　location　of　the　thin　N+-buried　layer　in　collector　region　is　investigated　in　detail.　The　result　show　that　the　FOM　of　f(T)　x　BVCEO　is　improved　and　the　device　temperature　decreases　as　the　N+-buried　layer　shifts　toward　SOI　substrate　insulation　layer.　The　approach　to　introducing　a　thin　N+-buried　layer　into　collector　region　provides　an　effective　method　to　improve　SOI　SiGe　HBT　overall　performance.