An infrared radiation element A heat insulating layer having sufficiently smaller thermal conductivity than a semiconductor substrate, is formed on a surface in the thickness direction of the semiconductor substrate. A heating layer, which is in the form of a lamina (plane) and has larger thermal conductivity and larger electrical conductivity than the heat insulating layer, is formed on the heat insulating layer. A pair of pads 4 for energization are formed on the heating layer. The semiconductor substrate is made of a silicon substrate. The heat insulating layer and the heating layer are formed by porous silicon layers having different porosities from each other, and the heating layer has smaller porosity than the heat insulating layer. By using the infrared radiation element as an infrared radiation source of a gas sensor, it becomes possible to extend a life of the infrared radiation source.