An experimental technique for the measurement of two-dimensional impurity diffusion profiles in silicon has been developed. Both the lateral and in-depth extent of dopant diffusion under a mask edge are magnified mechanically by sawing and angle lapping, and the magnified junction contour is delineated by chemical staining. The two-dimensional shape of the junction is reconstructed from the measured stained contour. A complete diffusion profile consisting of several isoconcentration contours can be obtained by measuring the junction shape on a series of samples with increasing substrate resistivities, provided the doping level in the substrate does not affect the diffusion of the impurity under study. Results of the two-dimensional diffusion of boron in silicon at 1050°C are presented.