The state-of-the-art RF and millimeterwave circuits design requires accurate prediction of the nonquasi-static (NQS) effects at high frequency for all levels of channel inversion. This paper provides a practical insight to help high-frequency performance assessment of ultrathin body and box fully depleted silicon-on-insulator MOSFETs through a powerful frequency normalization scheme. Frequency dependence of small signal characteristics derived from experimental S-parameters is analyzed and reveals that the transconductance efficiency (g(m)/I-D) concept, already adopted as a low-frequency analog figure-of-merit (FoM), can be generalized to high frequency, including under asymmetric operation. We report that the normalized frequency dependence of the generalized transadmittance efficiency (y(m)/I-D) FoM only depends on the mobility and inversion coefficient. In addition, this approach is also used to extract essential parameters such as the critical NQS frequency f(NQS).