The present invention provides a method of rounding the corner of the shallow trench isolation region, comprising the steps of: etching silicon substrate using a patterned mask layer and a pad oxide layer as an etch mask to form a trench in the silicon substrate, then removing part of the pad oxide layer, forming silicon dioxide on the surface of the silicon substrate in the trench, then removing part of the pad oxide layer and the silicon dioxide on the surface of the silicon substrate in the trench, repeating the step of oxidizing the surface of the silicon substrate and removing part of the pad oxide layer and silicon dioxide to round the corner of the trench, then performing the subsequent steps to form the shallow trench isolation region.