During the past five years great progress has been made in CV replacement metrology which utilizes precise dosing of electric charge on dielectric surfaces achieved with a corona discharge in air. This charge produces controlled changes of electric field in the dielectric film and in the space charge region of semiconductor substrate. The response of the dielectric and semiconductor is monitored in a non-contact manner using three measurements: the contact potential difference (CPD) in the dark, CPD under strong illumination, and the small signal ac-surface photovoltage (ac-SPV). In COCOS metrology these measurements are performed as a Junction of the corona charge placed on the whole wafer. A near equipotential, whole wafer surface is maintained while the semiconductor space charge is transferred from accumulation — through flat band — to deep inversion. Data analysis based on electrostatic equations and charge neutrality gives a total set of electrical parameters, equivalent to those obtained in MOS-CV metrology, characterizing the space charge, the semiconductor-dielectric interface and the dielectric film. The equipotential condition is crucial for reducing charge transport along the surface without creating guard-rings. Using a blanket of corona charge placed over the wafer surface and whole wafer mapping of CPD and SPV, the COCOS metrology enables one to obtain whole wafer maps of almost all parameters. Examples are given, illustrating COCOS application to Si/SiO2, with an emphasis on thin gate oxide reliability.