Ozone/TEOS thermal chemical vapor deposition (CVD) has been investigated for SiO2 deposition on Si, using a cold‐wall research reactor equipped to determine the effects of precursor concentration, deposition temperature (300–500 °C), and pressure (30–200 Torr) on deposition rates, etch rates, and step coverage in the regime of subatmospheric CVD (SACVD). Deposition rates first increase with substrate temperature then reach a maximum and finally decrease distinctly at higher temperatures, with the latter reflective of reactant depletion in the gas phase. Wet etch rates decrease at higher deposition temperature and higher ozone/TEOS ratio, indicating improved film quality under these conditions. Elevated deposition temperatures significantly improves step coverage in high‐aspect‐ratio trenches, but decreases deposition rates. Deposition rates increase and then saturate with TEOS concentration, suggesting rate‐limited behavior associated with lack of ozone.