A gate controlled structure is described. It is shown to be a convenient device for measuring mobility and concentration profile of majority carriers in diffused zones. The values of these two parameters are derived from measurements of gate capacitance and resistivity as a function of gate voltage. Various ways of obtaining C-V deep-depletion curves are discussed in order to justify the choice of a gate controlled structure. The measurement technique is discussed. Limitations of the method are due, on one hand, to the depletion approximation and, on the other hand, to an excessive reverse current across the diffused junction induced by the gate voltage. This effect is encountered especially in low-concentration samples, such as ours, in the range of 1015-1016cm-3. For illustration purposes, profiles of a p diffusion used in the MOSC process are measured at the beginning and at the end of the fabrication process.