The principles governing the plasma deposition of SiO2films for use as gate insulators ina‐Si thin‐film transistors (TFT’s) are discussed. A deposition arrangement is described which favors the reaction at the substrate over that in the discharge volume. It is shown that the variables leading to large values of the breakdown fieldEbkand to greatest stability of the flat band voltageVfbare the substrate temperatureTs, the gas flow ratio N2O/SiH4, and the ratio of the discharge half‐period to the transit time of the ions between the electrodes.a‐Si/SiO2TFT’s operated in the dc mode and in a mode simulating LC display operation show much less shift of the threshold voltageVththan doa‐Si/Si3N4TFT’s for equivalent gate fields.