A system and method are disclosed for determining the effective channel width (Weff) and the effective channel length (Leff) of metal oxide semiconductor devices. One advantageous embodiment of the method provides a plurality of metal oxide semiconductor field effect transistor capacitors in which each capacitor has a same value of drawn channel length but a different value of drawn channel width. A value of Fowler-Nordheim tunneling current is measured from each capacitor. Channel width offset is the difference between the drawn channel width and the effective channel width. A value of channel width offset is obtained from the measured values of the Fowler-Nordheim tunneling currents and used to determine the value of effective channel width. A similar method is used to determine the value of the effective channel length.