This paper proposes measurement method to separate the parasitic inductance and stray capacitance in the components of a power electronics circuit. This study focuses on time domain reflectometry (TDR), which is a high-speed transmission technique. In many cases, components mounted on power electronics circuits have parasitic parameters such as a parasitic inductance in series with a stray capacitance in parallel. It is important to separate these parameters into components of inductance and capacitance, as well as to determine their values in order to consider EMI prevention of particularly high power density mounted converters. This paper describes a method to measure the values of the parasitic inductance and stray capacitance individually by changing the characteristic impedance of a transmission line used in the TDR measurement method.