A method of reducing striation on a sidewall of a recess is provided. The method includes the steps of providing a substrate covered with a photoresist layer. Then, the photoresist layer is etched to form a patterned photoresist layer. Later, a repairing process is performed by treating the patterned photoresist layer with a repairing gas which is selected from the group consisting of CF4, HBr, O2 and He. Next, the substrate is etched by taking the patterned photoresist layer as a mask after the repairing process. Finally, the patterned photoresist layer is removed.