In　this　paper,　the　positive　influence　of　a　uni-traveling-carrier　(UTC)　structure　to　ease　the　contract　between　the　responsivity　and　working　speed　of　the　InP-based　double　hetero-junction　phototransistor　(DHPT)　is　illustrated　in　detail.　Different　results　under　electrical　bias,　optical　bias　or　combined　electrical　and　optical　bias　are　analyzed　for　an　excellent　UTC-DHPT　performance.　The　results　show　that　when　the　UTC-DHPT　operates　at　three-terminal　(3T)　working　mode　with　combined　electrical　bias　and　optical　bias　in　base,　it　keeps　a　high　optical　responsivity　of　34.72　A/W　and　the　highest　optical　transition　frequency　of　120　GHz.　The　current　gain　of　the　3T　UTC-DHPT　under　1.55-mu　m　light　illuminations　reaches　62　dB.　This　indicates　that　the　combined　base　electrical　bias　and　optical　bias　of　3T　UTC-DHPT　can　make　sure　that　the　UTC-DHPT　provides　high　optical　current　gain　and　high　optical　transition　frequency　simultaneously.