Abstract: Based on a 400 V power bipolar integrated device(BJT and a anti-parallel p-i-n diode integrated on the same chip) and through simulation and experimental test,some fundamental concepts and physical images were established concerning the influence of the parasitic lateral p-n-p transistor on the integrated device and the dependence of this influence on the distance between the main transistor and the internal diode.Finally,the optimized design of the above-mentioned distance was proposed.These provide a theoretical basis for understanding the issue and devising new methods to isolate the main transistor and the internal diode.