One of the methods to delineate a two-dimensional dopant profile in Si devices is the selective etching technique combined with imaging of the doping dependent topography by atomic force microscopy. A major problem of the etching procedures reported so far is the critical control of the etch duration of only a few seconds as well as a limited sensitivity and dynamic range. We report further improvements of the conventional technique and compare it to an alternative approach. Etching experiments were carried out in an electrolytic cell, whereby the etching is controlled potentiostatically. Better control of the dissolved volume is achieved through current integration. Buffered HF as the electrolyte replaces the difficult nitrogen related chemistry of the classical approach. The etch rates thereby decrease by a factor of 10-100 thus allowing for a longer etch duration. The basic mechanisms, the sensitivity, and the dynamic range of the two techniques have been studied by using homogeneous samples and special test structures for calibration and ultrashallow profiling. Two-dimensional profiling has been carried out on cross sections of 0.25 mu m complementary metal-oxide-semiconductor devices with the classical and the electrochemical approaches. Problems of preparation, etching procedure, and imaging techniques are discussed in order to improve the quantification of the selective etching technique.