The SPICE-aided electrothermal analysis of a self-excited push–pull DC–DC converter is considered in the paper. The new electrothermal model of a pulse transformer, which constitutes the basic component element of the considered converter, is proposed. This model contains among others: two different temperatures of the windings and the core, the influence of temperature on losses in the core and in the windings, the dependence of the magnetization curve on the core temperature, the Curie temperature, selfheating and mutual thermal interactions between the core and the windings. The semiconductor devices are described with the use of the hybrid electrothermal models. The measurements and electrothermal calculations of the characteristics of the investigated converter with the use of the models proposed in the paper are performed. A good agreement between the results of the calculations and the measurements achieved with this model testifies to correctness of the presented models.