An　InP/InGaAsP　uni-traveling-carrier　double　heterojunction　phototransistor　(UTC-DHPT)　photodetector　is　simulated　and　analyzed　in　a　two-dimensional　(2D)　model　utilizing　a　numerical　device　simulator　(Atlas).　The　effects　of　device　structure　parameters　on　operational　performance,　such　as　responsivity　and　characteristic　frequency,　are　studied　in　detail.　Simulation　results　indicate　that　the　UTC-DHPT　can　ease　the　contradiction　between　detection　efficiency　and　working　speed,　which　exists　in　traditional　heterojun-ction　phototransistor　and　achieve　both　high　responsivity　(＞=　17.93　A/W)　and　high　characteristic　frequency　(＞=　121.68　GHz)　simultaneously.