A manufacturing method of a semiconductor device which can decrease the degradation of an element due to plasma in the LDD formation process is provided. The degradation of an element due to plasma is decreased by forming an element having an LDD structure according to a manufacturing method of a semiconductor device using a hard mask. Covering the substrate by an electrically conductive film allover, the density of electric charge accumulated in a gate electrode in the plasma process such as anisotropic etching can be reduced, and the degradation due to plasma process can be reduced.