Abstract: A microwave integrated circuit internal-node waveform probing arrangement using a portable ungrounded voltage sensing probe and a commercially available transition analyzer instrument are disclosed. Harmonic frequency and phase processing are accomplished on the probe sensed voltage waveforms from internal nodes of for example a C-band monolithic microwave integrated circuit (MMIC) power amplifier circuit device. The disclosed probing is applied to determining signal voltage and signal current flow waveforms for the MMIC device. Examples relating to use of the invention to analyze operation of microwave circuits and prevent premature device failures are included; these include variation of waveforms as a function of frequency, drive and measurement location in a device. The potential impact of the disclosed technique includes MMIC design verification, in-situ device model extraction, process diagnosis, and reliability assessment.