A manufacturing method of a semiconductor memory device includes forming a first gate electrode having a charge storage layer, a block layer, and a control gate electrode on a first region of a semiconductor substrate, forming a second gate electrode on a second region of the semiconductor substrate, forming a protective insulating film on a side surface of the block layer, exposing the first region while covering the second region on the semiconductor substrate with a photoresist, using the photoresist, the first gate electrode, and the protective insulating film as masks to implant an impurity into the first region of the semiconductor substrate, and removing the photoresist by wet etching which uses a mixed solution containing H2SO4 and H2O2. The protective insulating film having an etching selective ratio of 1:100 or above with respect to the photoresist under wet etching conditions using the mixed solution.