A method of manufacturing a semiconductor device includes forming on a lower insulating layer first to third electrically conducting layers sequentially, forming a mask pattern on the third conducting layer, dry-etching the first to third conducting layers with the mask pattern as a mask, thereby dividing the conducting layers, and forming an insulating layer between the adjacent second conducting layers by an HDP-CVD process so that a void is defined so as to be located lower than an interface between the first and second conducting layers and higher than an interface between the second and third conducting layers so as to have a sectional area larger than the second conducting layer. The forming of the insulating layer by the HDP-CVD process includes burying the insulating layer and sputtering to spread a frontage of a buried region buried by the burying process, both burying and sputtering being repeated alternately.