A method of forming a contact opening in a semiconductor substrate is presented. A plurality of trench gates each having a projecting portion are formed in a semiconductor substrate, and a stop layer is deposited over the semiconductor substrate extending over the projecting portions, wherein each portion of the stop layer along each of the sidewalls of the projecting portions is covered by a spacer. By removing the portions of the stop layer not covered by the spacers by utilizing a relatively higher etching selectivity of the stop layer to the spacers, the openings between adjacent projecting portions with an L-type shape on each sidewall can be formed, and a lithography process can be performed to form self-aligned contact openings thereafter.