This article presents the results of computer analysis of selected switching networks. In these analyses, the influence of selected parasitic components of electronic switches on the total and active power losses in these switches is considered. Analyses are performed using the SPICE software for two models of semiconductor switches: an ideal switch with RC parasitic components and the SPICE model of an IGBT. The influence of parasitic capacitances and resistances of these devices operating with the control signal of different parameters values on the total and active power dissipated in these switches is analyzed. On the basis of the obtained computations the average and peak-to-peak values of the junction temperature of electronic switches at the steady state are calculated using a compact thermal model. It is shown that parasitic elements visibly influence waveforms of the active and total power. It is proved that the simplified model using the total power in computations of the junction temperature makes it possible to obtain a high accuracy of computations only in a situation when the transistor operates with a resistive load. For an inductive load, such simplification can cause an unacceptably high computation error exceeding even 30%. Such an error is a result of big differences between the active and total powers during switching-on and switching-off processes.