Some of the important factors that affect the degree of reproducibility of desired dimensions, flatness, and surface finish of chemically etched silicon have been investigated. The etching rate of single crystal silicon in hydrofluoric and nitric acids was studied as a function of the ratio of the concentrated acids, temperature, and stirring rate. These variables were found to be related to the etching rates over the ranges studied. No difference in etch rate was observed for n, p and n‐p junction silicon, ranging in resistivity from 0.05 to 78 ohm‐cm. The etch rate appears to be dependent on the diffusion of the fluoride species to the silicon surface in the nitric acid‐rich region. The controlled etching technique has been applied to the etch‐cutting of wafers from selectively masked silicon slices. Preliminary investigation has shown that this method is applicable for the preparation of slices for diffusion processing.