A method for forming spacers of different sizes includes the following steps. First a substrate is provided, which has a first element, a second element, a first material layer and a second material layer thereon. A first dry etching is performed to remove part of the second material layer to form a first spacer by the first element and to form a second side wall by the second element, so that the first material layer between the first spacer and the second side wall is exposed to become a damaged first material layer. A trimming procedure is performed to trim the damaged first material layer. A mask is used to cover the first element, the first spacer and part of the first material layer then a wet etching is performed to remove the second side wall.