Intentionally oxygen‐doped Mo films false(MoOxfalse) for MOS gate electrodes are investigated to eliminate the penetration of implanted As ions into the silicon substrate through the gate electrodes and gate oxides. The MoOx films are prepared by reactive sputtering of Mo in a mixture of Ar and O2 gases. Depth profiles of As ions and MOS C‐V curves are measured to estimate stopping properties. For as‐deposited MoOx films, whose oxygen concentrations are higher than 20 atom percent (a/o), As ion penetration depth is within 0.15 μm under 100 keV As ion implantation. This depth is about one third of that in normal Mo films. This excellent stopping property can be attributed to the nearly amorphous structure, which suppresses As ion channeling in the films resulting from oxygen doping. The resistivity of MoOx films with 39 a/o oxygen after annealing at 1000°C for 30 min is 25 μΩ‐cm, which is only three times as large as that for normal Mo films. In MoOx gate MOS structures, MOS characteristics are independent of oxygen concentrations in the films, and are almost the same as the characteristics for normal Mo gate electrodes.