Dopant concentration sensitive etching of silicon in HF:HNO3:CH3COOH solution was studied using epitaxially grown silicon samples. The study has shown the unstable character of the process, significant time and structure size dependencies of the etching rate, as well as the dependence of the rate on the dopant concentration gradient. The data may be rationalized on the basis of the electrochemical and autocatalytic nature of the reaction. The influence of the dopant gradient and overall device geometry on the etching rate may cause significant inaccuracy of the dopant distribution measurements.