In　order　to　enhance　the　breakdown　voltage　of　third-generation　SiGe　HBTs　at　no　expense　of　RF　performance　and　current　handling　capability,　the　superjunction　(SJ)　structure　is　studied.　It　is　shown　that　the　depth　of　SJ　should　be　designed　carefully　and　cannot　exceed　18%　of　the　total　width　of　collector-base　space　charge　region.　Furthermore,　a　novel　double　SJ　layers　structure　with　unequal　depth　is　presented,　which　could　effectively　improve　avalanche　behavior　with　an　increase　6.7%　in　BVCBO　and　33.3%　in　BVCEO.