Degradation of ESD avalanche diodes breakdown voltage (BV) characteristics in electrical overstress (EOS) regimes is observed and studied in BCD process technology. Both walk-in and walk-out effects are studied as a function of device structure parameters. It was shown that, in constant current avalanche stress regime, the level and direction of BV degradation can be controlled by changing the RESURF poly plate. High current breakdown TLP characteristics have been analyzed for the same phenomena