Single port characterization of RF amplifier phase and amplitude transfer functions are developed by measuring the output of the amplifier as it is excited by a predetermined frequency over a series of bias steps. One bias step is chosen as a reference level. Amplitude characterization is obtained from measured magnitude at each step in the test sequence. Phase information is extracted from the same measurements by measuring phase and phase trajectory at a reference level, and subtracting measured phase information at a desired step in the test sequence from an estimation of the reference phase trajectory at that step. Reference measurements may be interspersed with other measurements.