On-chip silicon-integrated and PWB-integrated transformers are currently being developed for signal and power applications in high-frequency power supplies. Prototype transformers feature relatively high winding resistances, core loss, and leakage inductances compared to conventional transformers. Short-circuit tests have limited use for characterizing these prototype high-parasitic transformers. In this paper, series-coupling tests are developed and applied for the accurate characterization of the resistive and inductive elements of on-chip silicon-integrated and PWB-integrated prototype transformers. In the series-coupling tests, the various resistive and inductive components, simply sum together making transformer characterization more direct and robust than attempting to interpret the short-circuit tests. Experimental results are validated by finite-element simulation.