Deep depletion MOS C(V) curves obtained by reverse biasing the junctions of MOSFET's are analyzed to produce N (X) doping profiles. Analytical techniques and possible errors are discussed together with experimental results obtained from samples on bulk, ion‐implanted, and epitaxial Si wafers. Experimental results are compared with spreading resistance measurements. The simplicity of the method makes it suitable for rapid impurity profile research and process control applications.