A method of manufacturing a polysilicon (poly-Si) layer, a method of manufacturing an organic light-emitting display apparatus using the method, and an organic light-emitting display apparatus manufactured by using the method. The method includes forming an amorphous silicon (a-Si) layer on a substrate having first and second areas, thermally treating the a-Si layer to partially crystallize the a-Si layer into a partially crystallized Si layer, removing a thermal oxide layer through a thermal treatment, selectively irradiating the first areas with laser beams to crystallize the partially crystallized Si layer.