A method of manufacturing a transistor and a method of manufacturing an organic electroluminescence display are disclosed. When an amorphous silicon layer is crystallized, a silicon oxide layer formed on a polysilicon layer is subsequently patterned. Impurity ions are implanted into first and second regions of the amorphous silicon layer to form first and second doped regions. The silicon oxide layer is patterned so that the silicon oxide layer may be removed from an ohmic contact region of the polysilicon layer, and covers only a channel region of the polysilicon layer.