Semiconductor device

According to one embodiment, a semiconductor device includes an element region, an element isolation region adjacent to the element region, a gate insulating layer provided on an upper surface of the element region, and a gate electrode including a semiconductor layer, the semiconductor layer containing boron (B) and including a portion provided on the gate insulating layer, the element isolation region including an upper portion including an upper surface of the element isolation region and a lower portion including a lower surface of the element isolation region, and the upper portion of the element isolation region applying compressive stress to a portion of the element region, which is adjacent to the upper portion of the element isolation region.