One　method　of　non-uniform　finger　spacing　is　proposed　to　enhance　thermal　stability　of　multiple　finger　power　heterojunction　bipolar　transistor.　Using　coupling　thermal　resistance　to　characterize　the　influence　of　the　change　of　emitter　spacing　on　thermal　coupling,　the　relation　between　coupling　thermal　resistance　and　emitter　spacing　is　obtained.　Temperature　distribution　on　the　emitter　fingers　of　multi-finger　heterojunction　bipolar　transistor　is　studied　by　a　numerical　electro-thermal　model.　The　results　show　that　the　heterojunction　bipolar　transistor　with　non-uniform　finger　spacing　has　a　smaller　temperature　difference　between　fingers　thant　the　traditional　uniform　finger　spacing　heterojunction　bipolar　transistor　under　the　same　power　dissipation.　So　the　method　of　non-uniform　finger　spacing　is　very　effective　to　enhance　the　thermal　stability.