In one embodiment, a method for extracting C-V characteristics of ultra-thin oxides includes coupling a device under test to a testing structure, in which the device under test includes a plurality of transistors. Alternatively, the device under test includes a plurality of varactors. The method further includes inputting a radio frequency signal of at least one GHz into the testing structure, de-embedding the parasitics of the testing structure, inputting a bias into the device under test, determining the capacitance density per gate width of the device under test, plotting capacitance density per gate width versus gate length to obtain a first curve, and determining a slope of the first curve. These steps are repeated for one or more additional biasing conditions, and the determined slopes are plotted on a capacitance density per voltage graph to obtain a C-V curve for the device under test.