Thin molybdenum films ∼1000 Å deposited on thermal SO2grown on Si are observed to act as partial masks for B diffusion. B‐doped glass is used as a diffusion source. Detection of the diffusion front is through measuringC‐Vcurves for the MOS structure with molybdenum as the metal electrode. The above process is used to fabricate low threshold enhancement mode and depletion modep‐channel MOSFET's in one diffusion step.