The input, output and reverse transfer capacitance of power MOSFETS (Ciss, Coss and Crss respectively) are critical device parameters for switching applications.  Unfortunately, the DC voltages applied to power MOSFETs during many switching applications are in the hundreds or even thousands of volts; this has made the measurement of these parameters under specified DC bias voltage conditions impossible using conventional capacitance meters.  The Agilent B1505A Power Device Analyzer/Curve Tracer supports a high-voltage source/monitor unit (HVSMU), a multi-frequency capacitance measurement unit (MFCMU) and a high-voltage bias-T that permit direct measurement of high-power MOSFET capacitance measurement.  This solution makes it easy to directly measure Ciss, Coss and Crss at DC bias voltages of up to 3000 V.  This application note explains the theory behind these measurements and illustrates the measurement techniques required to make these measurements using Agilent B1505A.