PURPOSE: To enable the diffusion depth of impurity to be enhanced in accuracy and monitored through a non-destructive manner when impurities are diffused into a semiconductor from a solid diffusion source.

CONSTITUTION: A device is composed of a semiconductor wafer where at least two epitaxial layers 2 and 3 or more layers of different materials or different from each other in carrier concentration are formed, a solid diffusion source 6 formed on the wafer, and a metal electrode 20 provided onto the solid diffusion source 6, wherein a measuring circuit equipped with a bias voltage applying system 31 which applies a bias voltage between the metal electrode 2 and a semiconductor substrate and a diffusion depth measuring system 32 which is able to measure a capacitance between them is provided, so that impurities can be diffused measuring a capacitance between a metal electrode and a semiconductor substrate. By this setup, the diffusion depth of impurities can be monitored through a non-destructive method while a impurity diffusing process is carried out, so that impurity diffusion can be enhanced in controllability, and a wafer is protected against damage, and consequently an impurity diffusion process can be automated.