Taking　into　account　of　the　temperature　dependence　of　base-emitter　voltage　and　the　additional　ballasting　resistor　in　emitter,　an　improved　three-dimensional　thermal-electrical　model　is　presented　to　study　the　temperature　distribution　in　power　heterojunction　bipolar　transistor　(HBT).It　is　found　that　multi-finger　HBT　with　uniform　emitter　ballasting　resistor　exhibits　a　higher　temperature　at　the　center　of　the　device,　which　reduces　the　power-handing　capability　of　HBT.　Therefore,　non-uniform　emitter　ballasting　resistor　design　of　multi-finger　power　HBT　is　presented　to　improve　the　power-handing　capability　of　HBT.　Taking　12-finger　Si0.8Ge0.2　HBT　for　example,　the　design　procedure　of　non-uniform　emitter　ballasting　resistor　is　described　in　detail.　Compared　with　the　uniform　design,　the　center　finger　temperature　reduces　obviously　and　the　device　temperature　distribution　is　uniform　with　the　design　of　non-uniform　emitter　ballasting　resistor　under　the　condition　that　the　total　emitter　ballasting　resistance　is　the　same.　Furthermore,　it　is　found　that　the　temperature　distribution　is　more　uniform　with　the　exponential　variation　of　emitter　ballasting　resistance.　As　a　result,　the　power-handing　capability　of　HBT　is　improved　obviously,　which　is　beneficial　to　the　design　of　power　HBT.