The　temperature　characteristics　of　SiGe　HBT　and　its　reliability　under　thermal　stress　are　studied.　The　experiment　results　indicate　that　the　current　gain　at　77K　is　much　larger　than　the　one　at　290K.　And　there　is　a　critical　value　of　Ic,　which　is　2xl0-4A.　Over　this　value,　the　gain　increases　with　the　decrease　of　the　temperature.　But　below　the　value,　the　gain　drops　with　the　decrease　of　the　temperature.　The　current　ideal　factor　is　smaller　than　2　when　the　temperature　is　over　193K,　but　larger　than　2　at　193K　or　below.　Besides　this,　the　thermal　stress　experiments　for　the　base-emitter　junction　were　taken　under　100C　and　150C,　and　the　stress　time　was　90　hours　and　30　hours,　respectively.　The　experiment　results　indicate　that　the　device　characteristic　parameters　fluctuate　under　the　different　thermal　stress　conditions.　The　annealing　and　degeneration　play　the　collective　role　in　the　characteristics　fluctuating　under　the　thermal　stresscondition.　©2009　IEEE.