This　letter　proposes　that　dominant　mechanism　that　induces　the　change　of　traps　and　defects　in　AlGaN　barrier　layer　varies　with　different　range　of　voltage　stress　on　the　gate　of　AlGaN/GaN　high　electron　mobility　transistors.　The　gate-source　(drain)　reverse　current-voltage　(I-V)　and　capacitance-voltage　(C-V)　characteristics　were　measured　after　each　voltage　stress　applied　to　the　gate　which　stepped　from　-8　to　-70　V　in　-1　V　step.　They　showed　similar　changes　in　test,　both　decreased　from　-8　to　-20　V　and　increased　from　-20　to　-70　V.　The　micro-Raman　spectroscopy　focused　on　GaN　layer　was　measured　before　stress,　during　-30　V　stress,　and　after　-70　V　stress,　respectively.　They　kept　constant　in　the　measurement.　It　proved　that　inverse　piezoelectric　effect　had　few　influence　in　GaN　layer.　The　increase　of　filled　inherent　traps　and　permanent　defects　in　AlGaN　barrier　layer　after　different　voltage　stress　accounted　for　the　experimental　phenomenon.　The　former　was　due　to　gate　electron　injection　which　played　a　main　role　in　low　bias　stage,　the　latter　was　due　to　inverse　piezoelectric　effect　which　played　a　main　role　in　high　bias　stage.