A process for forming shallow trench isolation region with corner protection layer. A protection layer is formed within the opening that defines the isolation trench as part of the etching mask such that the etching rate of the protection layer is less than the mask layer and the pad insulating layer to the etchant used to remove the mask layer and pad insulating layer. The protection layer is partially removed and left adjacent to the shallow trench isolation region as a corner protection layer after removing the mask layer and pad insulating layer. Thus, the indentation next to the corner of the isolation region is avoided.