According to one embodiment, a semiconductor device, includes: a first semiconductor region of a first conductivity type; a second semiconductor region provided on the first semiconductor region, an impurity concentration of the second semiconductor region being lower than an impurity concentration of the first semiconductor region; a third semiconductor region of a second conductivity type provided on the second semiconductor region; and a fourth semiconductor region provided on the third semiconductor region or in a portion of the third semiconductor region. A lattice strain of the fourth semiconductor region is greater than a lattice strain of the third semiconductor region.