As　is　well　known,　there　exists　a　tradeoff　between　the　breakdown　voltage　BVCEO　and　the　cut-off　frequency　f(T)　for　a　standard　heterojunction　bipolar　transistor　(HBT).　In　this　paper,　this　tradeoff　is　alleviated　by　collector　doping　engineering　in　the　SiGe　HBT　by　utilizing　a　novel　composite　of　P+　and　N-　doping　layers　inside　the　collector-base　(CB)　space-charge　region　(SCR).　Compared　with　the　single　N-type　collector,　the　introduction　of　the　thin　P+　layers　provides　a　reverse　electric　field　weakening　the　electric　field　near　the　CB　metallurgical　junction　without　changing　the　field　direction,　and　the　thin　N-　layer　further　effectively　lowers　the　electric　field　near　the　CB　metallurgical　junction.　As　a　result,　the　electron　temperature　near　the　CB　metallurgical　junction　is　lowered,　consequently　suppressing　the　impact　ionization,　thus　BVCEO　is　improved　with　a　slight　degradation　in　f(T).　The　results　show　that　the　product　of　f(T)　x　BVCEO　is　improved　from　309.51　GHz.V　to　326.35　GHz.V.