Optical channel waveguides have been fabricated into integrated circuit lithography mask plates by silver‐sodium ion exchange. The process combines the advantages of Ag thin‐film ion sources and the accurate and reliable patterning of chromium films on mask plates. The process is potentially suitable for cheap mass production, since no lithography is needed during the actual waveguide fabrication. The tailoring of waveguide cross sections by modifying the electric field distribution inside the glass is also presented.