The present invention provides a manufacturing method of a semiconductor device, and relates to the semiconductor technology field. The method comprises the steps of providing a semiconductor substrate on which a plurality of pseudo grids are formed; orderly depositing a grinding stop layer and an interlayer dielectric layer to cover the semiconductor substrate and the plurality of pseudo grids, wherein the top surface of the interlayer dielectric layer is higher than the top surfaces of the pseudo grids; carrying out the first chemical mechanical grinding on the interlayer dielectric layer and stopping in the grinding stop layer; carrying out the second chemical mechanical grinding on the interlayer dielectric layer and stopping on the top surfaces of the pseudo grids; carrying out the third chemical mechanical grinding on the interlayer dielectric layer, wherein a liquid comprising an oxidizing agent is added during the third chemical mechanical grinding process to oxidize the top surfaces of the pseudo grids to form a protection layer. According to the manufacturing method of the present invention, the hydrogen peroxide is used during the third chemical grinding process to oxidize the top surfaces of the pseudo grids to form the protection layer, and further the materials of the pseudo grids are protected from losing in a later cleaning step.