A semiconductor device includes: two first semiconductor regions of a first conductivity type spaced apart from each other; a second semiconductor region of a second conductivity type provided between the two first semiconductor regions; a first insulator region surrounding the two first semiconductor regions and the second semiconductor region; a third semiconductor region of the second conductivity type; a fourth semiconductor region of the second conductivity type, the fourth semiconductor region surrounding the third semiconductor region and the first insulator region and having an impurity concentration of the second conductivity type lower than an impurity concentration of the third semiconductor region; a second insulator region that surrounds the fourth semiconductor region; a conductor layer provided over the second semiconductor region; two first contact plugs; a second contact plug provided on the conductor layer; and a third contact plug provided on the third semiconductor region.