The dependence of the electrical and optical properties of reactively evaporated indium tin oxide films on substrate temperature and tin concentration has been studied. Films of resistivity as low as 3 x 10-4 Ω cm and high visible transparency of about 91% have been obtained at higher deposition temperatures (∼300 °C) for tin concentrations of 10-1 5 wt% in the source alloy. Hall mobility in the films has been found to decrease with the addition of tin and increase with deposition temperature. An observed increase in carrier density with substrate temperature has been viewed as being due to the possibility that higher deposition temperature favours the incorporation of tin as Sn4- in the films. In the optical band-gap calculation the effect of collision broadening, which is typical for a degenerate semiconductor, has been included and found to be significant. © 1989 IOP Publishing Ltd.