A review of the principal techniques used for the extraction of MOS transistor parameters from static, dynamic and transient current measurements is proposed. More specifically, the procedure for the extraction of the main MOSFET parameters such as effective dimensions, threshold voltage, mobility, mobility attenuation factor, source-drain series resistance, channel doping etc., from the static transfer characteristics is presented. Methods for the evaluation of fast and slow interface trap and bulk deep level densities, using the subthreshold slope, dynamic transconductance, charge pumping current, low frequency noise and drain current transient are described. The specificity and resolution of each technique are discussed. The peculiarities of very small area MOS transistors, in which the active number of defects becomes close to unity, are also given.