An object of one embodiment of the present invention is to provide an antifuse which has low writing voltage. The antifuse is used for a memory element for a read only memory device. The antifuse includes a first conductive layer, an insulating layer, a semiconductor layer, and a second conductive layer. The insulating layer included in the antifuse is a silicon oxynitride layer formed by adding ammonia to a source gas. When hydrogen is contained in the layer at greater than or equal to 1.2×1021 atoms/cm3 and less than or equal to 3.4×1021 atoms/cm3 or nitrogen is contained in the layer at greater than or equal to 3.2×1020 atoms/cm3 and less than or equal to 2.2×1021 atoms/cm3, writing can be performed at low voltage.