In this paper we report on the use of expanding thermal plasma technique for the deposition of carbon-free silicon dioxide films by means of argon/hexamethyldisiloxane/oxygen mixtures, at growth rates in the range of 6–12 nm/s, as a function of the substrate temperature. The variation of substrate temperature has been investigated as an alternative route to ion bombardment in promoting the densification of SiO2-like films. Information concerning film chemical composition was obtained by means of Fourier transform IR absorption and X-ray photoelectron spectroscopies. The films are stoichiometric and a residual hydrogen content of 3.5·1021 at/cm3 is detected in the film deposited at 300 °C (SiO2H0.17). The film optical characterization by means of UV–VIS and IR spectroscopic ellipsometry has highlighted the beneficial role of substrate temperature in the densification of the SiO2 film matrix and the decrease of film porosity.