The embodiment of the invention provides a uni-traveling carrier photodiode. The wet nitrogen oxidation process is carried out on a partial structure in a traditional collection region to obtain a part of oxidation type collection region. Because the refractive index of an oxide insulating layer formed by the partial structure of the oxidation process is low, the parasitic junction capacitance ofthe uni-traveling carrier photodiode is reduced, the RC time constant is reduced, and the response speed of the uni-traveling carrier photodiode is improved.