Semiconductor device

A semiconductor device comprising:

• a first insulating film comprising a first region, a second region, and a third region between the first region and the second region, wherein a thickness of the first insulating film in the third region is thicker than a thickness of the first region of the first insulating film and a thickness of the second region of the second region;
• a first oxide semiconductor film over the third region of the first insulating film;
• a second oxide semiconductor film over and in contact with the first oxide semiconductor film;
• a third oxide semiconductor film over and in contact with the second oxide semiconductor film;
• a second insulating film over the third oxide semiconductor film;
• a second gate electrode over the second insulating film and the first region and the second region of the first insulating film;
• and
• a first electrode and a second electrode each electrically connected to the second oxide semiconductor film,
• wherein a bottom surface of the second gate electrode is positioned lower than a bottom surface of the second oxide semiconductor film so that the second gate electrode faces a side surface of the second oxide semiconductor film with the second insulating film interposed therebetween.