Antireflective MoSi (AR‐MoSi) photomasks which are produced by applying a thin layer of MoSi oxide directly over the conventional MoSi layer on a quartz substrate has been developed. The thin layer of MoSi oxide is deposited using magnetron dc sputtering. The reflectivity and optical density of the thin layer are not affected by H2SO4at 120 °C. The layer reflectivity is changed by varying the oxygen partial pressure ratio in argon gas and the layer thickness. To obtain minimum reflectivity, the mechanism of antireflection was studied by using a model of multipath interference with absorption of light. Experimental and theoretical results are in good agreement and show a minimum reflectivity of 6.4% for a 40–60 nm thick MoSi oxide layer. By exposing the photomask, it was found that the AR‐MoSi photomask has practicable resolution performance comparable to conventional photomasks.