We investigate the origin of fabricated nanogap width variations using the electromigration method during metal deposition. This method also facilitates improved control over the nanogap width. A large suppression in the variation is achieved by sample annealing at 373 K during the application of bias voltages for electromigration, which indicates that the variation is caused by structural changes. This electromigration method during metal deposition for the fabrication of an accurate 1-nm gap electrode is useful for single-molecule-sized electronics. Furthermore, it opens the door for future research on integrated sub-1-nm-sized nanogap devices. (C) 2016 The Japan Society of Applied Physics