The　high　resistivity　substrate　of　1000　Ω·cm　was　employed　to　improve　the　high　frequency　performances　of　SiGe　HBT.　After　the　structure　of　device　was　introduced,　the　principle　of　how　the　substrate　affects　the　high　frequency　performances　of　the　device　was　analyzed　based　on　the　equivalent　two-port　network　model.　The　characteristics　of　fT　and　fmax　versus　the　resistivity　of　the　substrate　were　analyzed.　Tested　results　indicate　that　the　fT　and　the　fmax　of　the　device　based　on　the　high　resistivity　substrate　are　28%　and　47.7%　larger　than　that　of　the　one　based　on　the　conventional　N+　substrate　respectively.　This　shows　that　the　parasitic　capacitor　network　made　by　the　substrate　can　be　reduced　greatly　when　the　high　resistivity　substrate　is　employed.　More　ever,　the　minimum　noise　figures　were　deduced　and　measured.　The　results　show　that　the　minimum　noise　figure　of　SiGe　HBT　based　on　the　high　resistivity　substrate　has　almost　not　been　deteriorated　at　low　frequency,　but　slightly　higher　at　high　frequency　than　that　of　one　based　on　the　n+　substrate.