A　novel　design　of　SOI　SiGe　HBTs　with　a　buried　n(+)　thin　layer　and　p(-)　doping　layer　is　proposed　to　improve　the　product　of　cutoff　frequency　and　breakdown　voltage,　which　is　a　vital　Johnson＇s　figure　of　merit　(J-FOM)　of　the　device.　In　this　design,　the　n(+)　thin　layer　is　used　to　increase　the　cutoff　frequency　and　the　p(-)　doping　layer　is　adopted　to　maintain　a　high　breakdown　voltage.　Furthermore,　the　thickness　of　n(+)　thin　layer　is　also　studied　to　improve　the　J-FOM.　As　a　result,　for　the　novel　SOI　SiGe　HBT,　the　J-FOM　is　increased　from　351.5GHz-V　to　482.3GHz-V,　when　compared　with　that　of　the　traditional　device.　This　design　effectively　develops　the　application　of　SOI　SiGe　HBTs　in　microwave　power.