We investigate the radiation hardness of metal-oxide-semiconductor (MOS) capacitors with tungsten polycide (WSi/sub x/) and those with cobalt polycide (CoSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as gate electrode materials. CoSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has been considered as a gate/contact material for MOS devices in 0.18 μm integrated circuit fabrication due to its low resistivity and good thermal stability. However, we found that MOS capacitors with a CoSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate electrode exhibited an increase in radiation-induced interface trap density shift of more than one order of magnitude, and more than eighteen times larger in radiation-induced flatband voltage shifts compared with those with the WSi/sub x/ gate electrode, after 1 Mrad Co/sup 60/ /spl gamma/-ray irradiation under no applied bias.