A semiconductor device includes groove-like regions that are formed between two adjacent bit lines among a plurality of bit lines each having upper and side surfaces covered with a cap insulating film and a side-wall insulating film, respectively, a SiON film that contains more O (oxygen) than N (nitrogen) and continuously covers inner surfaces of the groove-like regions, and a silicon dioxide film formed by reforming polysilazane and filled in the groove-like regions with the SiON film interposed therebetween.