Etching of silicon dioxide in CF4 plasmas was theoretically investigated, and thereon a mathematical model to describe the etching process was formulated. By using a Langmuir-type surface chemistry model shown in the literature and the plasma chemistry model from our previous work, the etch rate was derived as a function of the discharge power. The data of the etch rate of silicon dioxide in CF4 plasmas in the literature were analyzed based on this etch model. As a result of this analysis, a linear relationship between the reverse etch rate and the reverse discharge power was found, which verifies the model and leads to another finding that the ion energy flux to the etch surface is proportional to the discharge Fewer. The intercept and gradient of the linear relation give estimates for the gradient of etch rate at zero discharge power and the etch rate at the infinite discharge power, respectively. These estimated values are found to depend on the flow rate. Based on this analysis, a mathematical form of the etch rate as a function of the flow rate of the feedstock gas was obtained and shown to be fairly close to the experimental results in the literature.