A method for manufacturing a semiconductor device comprises the following steps: etching a silicon oxynitride layer, a second silicon oxide layer, a second etching terminating layer and a first silicon oxide layer in sequence, stopping etching on a first etching terminating layer and forming a connecting pore; coating a bottom anti-reflection coating (BARC) in the connecting pore and on the surface of the silicon oxynitride layer; coating a first photoresist layer on the surface of the BARC and patterning the first photoresist layer; etching back the BARC in the connecting pore; removing the first photoresist layer; coating a second photoresist layer on the exposed surface of the BARC and patterning the second photoresist layer; and taking the patterned second photoresist layer as the mask to etch a trench to form the trench, wherein the BARC fills the connecting pore; the opening of the patterned first photoresist layer corresponds to the connecting pore; and the opening of the patterned second photoresist layer is the width of the trench. When the patterned photoresist is utilized to define the position of the trench, the method can enlarge the control window of the exposure machine and solve the fence defect in the trench.