A method of calculating as‐deposited elemental film composition during the actual deposition process was developed using optical emission spectroscopy of the glow discharge. These results are demonstrated by analyses of a series of thin film Ag1−xSixalloys fabricated using radio frequency sputter deposition with composite Ag+Si sputter targets. Using intensity ratios of the Si (251.6 nm), Ag (328.1 nm), and Ar (419.8 nm) emission lines after equilibration of the substrate temperature, estimates of at. % Si in the films were calculated which agreed well with post‐deposition composition measurements of the films by Auger electron spectroscopy. ©1995 American Institute of Physics.