A semiconductor device of the invention includes: a silicon island on a substrate having an insulating surface, the silicon island comprises a source, a drain and a ditch between the source and the drain; a gate electrode configured adjacent to the ditch, a gate insulating layer is provided between the gate electrode and the ditch; an adulteration region having an adulterating concentration lower than the concentration of the source and the drain which is configured between the ditch and at least one of the source and the drain; and a silicon nitride-containing layer on the gate electrode and the silicon island, which comprises a section contacted with the gate insulating layer having a first section on the ditch and a second section on the adulteration region, in which the second section has a thinner thickness than the first section. |