The invention discloses a manufacturing method of a semiconductor device. The manufacturing method comprises the steps of providing a semiconductor substrate, wherein the semiconductor substrate comprises a first region, the first region is provided with a stacked gate structure, the stacked gate structure comprises a floating gate, an inter-gate dielectric, a control gate, a mask layer and a buffer oxidation layer which are stacked in sequence form the bottom up, depositing a polycrystalline silicon layer on the semiconductor substrate, wherein the polycrystalline silicon layer covers the stacked gate structure, carrying out grinding on the polycrystalline silicon layer so as to expose the buffer oxidation layer, removing the buffer oxidation layer by adopting an etching process, and carrying out back-etching on the polycrystalline silicon layer. Grinding residues or polycrystalline silicon remains can be prevented from adhering to the control gate by adopting the manufacturing method disclosed by the invention.