The object of the present invention is to provide a ceramic substrate that can provide a substantially uniform temperature distribution to a surface of the ceramic substrate where a semiconductor wafer is treated. A ceramic substrate for a semiconductor-producing/examining device according to the present invention is a ceramic substrate having a conductor formed on a surface of the ceramic substrate or inside the ceramic substrate, wherein said substrate is containing oxygen and having a disc form, the diameter thereof exceeding 250 mm and a thickness thereof being 25 mm or less.