According to one embodiment, a semiconductor device includes a semiconductor layer, an element region provided on the semiconductor layer convexly, having a predetermined width in a first direction along a surface of the semiconductor layer, and extending in a second direction along the surface of the semiconductor layer and intersecting the first direction, a gate electrode arranged above the element region, a liner layer covering the gate electrode, and an element separation portion extends in the second direction on both sides of the element region in the first direction, and the liner layer continuously extends from the gate electrode to the element separation portion and the liner layer in the element separation portion lies below the element separation portion.