A method and apparatus for reducing the number of stages for measuring first and second switching speeds for PD/SOI transistors uses an inverter circuit which includes: a p-channel body-tied transistor; an n-channel body-tied transistor, coupled at their drains and gates; and a first and a second group of components tied to the bodies of the transistors. The first group restores body potentials for the transistors if the inverter circuit belongs to an even numbered stage of a ring oscillator. The second group provides body potentials for the transistors if the inverter circuit belongs to an odd numbered stage. After each transition of a waveform, the body potentials for the PD/SOI transistors are restored to the original potentials as stored in the capacitors. In this manner, a much smaller ring oscillator with fewer number of stages may be used to accurately measure the first and second switching speeds.