A semiconductor device of an embodiment includes: a first and second semiconductor regions of a first conductivity type; a third semiconductor region of a second conductivity type disposed between the first and second semiconductor regions; a fourth semiconductor region of the first conductivity type disposed below the first semiconductor region; a fifth semiconductor region of the first conductivity type disposed below the second semiconductor region; a first region containing carbon disposed between the first and fourth semiconductor regions; a second region containing carbon disposed between the second and fifth semiconductor regions; a third region disposed between the first and second regions; the first and second regions having a first and second carbon concentrations respectively, the third region not containing carbon or having a lower carbon concentration than the first and second carbon concentrations in a portion below an end of a lower face of a gate electrode.