The invention discloses a manufacturing method of a semiconductor device. The method comprises the following steps of: removing a pseudo-gate stack in the process of preparing a complementary metal-oxide-semiconductor (CMOS) transistor by using a replacement gate or gate last process; forming an L-shaped sidewall and a second sidewall on the L-shaped sidewall in a first opening which is formed after the pseudo-gate stack is removed; redefining the size of a replacement gate to play a role in adjusting the overlapped capacitance of a replacement gate stack and a source/drain region and a source/drain extension region; and forming a replacement sidewall by a sidewall of a gate electrode in the replacement gate stack, so that the overlapped capacitance of the sidewall and the source/drain region and the source/drain extension region is further reduced, and the whole overlapped capacitance of the device is further reduced. Furthermore, a device with a smaller size is obtained by a processmethod which is easier to implement.