In this paper, a physics-based, electro-thermal model for thepower diode turn-on is presented. The model, implementedin the circuit simulator SABER, is based on an approximationof the carrier distribution in the n-base of the diode usingsecond degree polynomials, resulting in a fast but accuratecalculation method. The turn-on physics is accuratelydescribed by taking into account low injection level as well asa correct transport equation for the minority carriers. Modelperformances are compared both to device numerical simulationsand measurements and show good agreements forvarious circuit and temperature conditions, as well as for differentdevice designs.