The present disclosure provides a semiconductor device and a fabrication method. The semiconductor device includes: a substrate; a first well region in the substrate, having first ions; an isolation layer in the first well region; a second well region and a third well region, formed in the first well region, located respectively on opposite sides of the isolation layer, having second ions with an opposite conductivity type as the first ions, and with a minimum distance from the isolation layer greater than zero; a first gate structure on the second well region and the first well region; a second gate structure on the third well region and the first well region; a barrier gate on the isolation layer, located between the first gate structure and the second gate structure, and having the second ions; and source-drain doped layers in the second well region and the third well region, respectively.