A method for fabricating a split gate of a memory device includes that a semiconductor substrate with a plurality of trenches and a protruding ridge; a first covering layer formed in the trenches and on the protruding ridge; the first covering layer is etched to form the thickness thereof between one tenth to one half of the depth of the trenches; a second covering layer is formed on the side walls of the trenches, on the first covering layer and on the protruding ridge; the second covering layer is etched so that the second covering layer on the side walls of the trenches and the protruding ridge is completely removed. The invention prevents the forming of cavities on the second covering layer filled into the trenches.