In　this　paper,　the　IC-VBE　characteristic　of　bipolar　transistors　are　described　by　novel　analytical　formulations,　which　for　the　first　time　present　the　expression　of　collect　current　in　the　second　fly-back　point.　Through　the　analytical　formulations,　it　is　found　that　a　smaller　emitter　ballast　resistance　can　make　the　collector　current　achieve　the　second　fly-back　point　before　transistors　are　burned-out,　and　then　returns　to　a　stable　situation.　Such　an　emitter　ballast　resistance　is　beneficial　to　both　of　the　output　power　and　thermal　stability　at　the　same　time.　The　experiment　result　also　verifies　our　conclusions.　©　2011　CJMW.