Based　on　the　thermal　network　of　the　two-dimensional　heterojunction　bipolar　transistors　(HBTs)　array,　the　thermal　resistance　matrix　is　presented,　including　the　self-heating　thermal　resistance　and　thermal　coupling　resistance　to　describe　the　self-heating　and　thermal　coupling　effects,　respectively.　For　HBT　cells　along　the　emitter　length　direction,　the　thermal　coupling　resistance　is　far　smaller　than　the　self-heating　thermal　resistance,　and　the　peak　junction　temperature　is　mainly　determined　by　the　self-heating　thermal　resistance.　However,　the　thermal　coupling　resistance　is　in　the　same　order　with　the　self-heating　thermal　resistance　for　HBT　cells　along　the　emitter　width　direction.　Furthermore,　the　dependence　of　the　thermal　resistance　matrix　on　cell　spacing　along　the　emitter　length　direction　and　cell　spacing　along　the　emitter　width　direction　is　also　investigated,　respectively.　It　is　shown　that　the　moderate　increase　of　cell　spacings　along　the　emitter　length　direction　and　the　emitter　width　direction　could　effectively　lower　the　self-heating　thermal　resistance　and　thermal　coupling　resistance,　and　hence　the　peak　junction　temperature　is　decreased,　which　sheds　light　on　adopting　a　two-dimensional　non-uniform　cell　spacing　layout　to　improve　the　uneven　temperature　distribution.　By　taking　a　2　x　6　HBTs　array　for　example,　a　two-dimensional　non-uniform　cell　spacing　layout　is　designed,　which　can　effectively　lower　the　peak　junction　temperature　and　reduce　the　non-uniformity　of　the　dissipated　power.　For　the　HBTs　array　with　optimized　layout,　the　high　power-handling　capability　and　thermal　dissipation　capability　are　kept　when　the　bias　voltage　increases.