The Si–SiO2 interface plays a key role in insulated-gate field-effect transistors (IGFETs). Of principal concern are the interface charge density Qic and the fast-state density Nfs. These properties can be optimized by eliminating the transition region and creating an abrupt interface. Our work with the chemical vapor deposition (CVD) of SiO2 using a CO2–SiH4–H2 system in the presence or absence of trace amounts of HCl gas at 1000°C has demonstrated that unannealed CVD SiO2 on (100) Si using a vertical-cold-wall reactor has properties similar to those of unannealed SiO2 on (100) Si formed by the usual thermal oxidation procedure. In addition, using only 2.27 vol% HCl, we have produced films of SiO2 on (111) Si that are better than their thermal counterparts, unannealed or annealed; i.e., Qic ≈ 5 × 1010 cm−2 and Nfs ≈ 1010 cm−2-eV−1. We attribute these results, at least in part, to an abrupt interface between the CVD SiO2 and Si. Deposition rates of 10 nm/min were used to reproducibly deposit 30–50 nm of SiO2. The CVD SiO2 films also show a significantly lower standard deviation in the breakdown fields (±1.5%) and the mobile charge densities (±5%) than their thermal counterparts. In general, Nfs was independent of Qic.