A method for manufacturing a dummy gate structure. The method may include: forming a dummy gate oxide layer and a dummy gate material layer on a semiconductor substrate sequentially; forming an ONO structure on the dummy gate material layer; forming a top amorphous silicon layer on the ONO structure; forming a patterned photoresist layer on the top amorphous silicon layer; etching the top amorphous silicon layer with the patterned photoresist layer as a mask, the etching being stopped on the ONO structure; etching the ONO structure with the patterned photoresist layer and a remaining portion of the top amorphous silicon layer as a mask, the etching being stopped on the dummy gate material layer; removing the patterned photoresist layer; and etching the dummy gate material layer, the etching being stopped at the dummy gate oxide layer to form a dummy gate structure.