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A silicon-controlled rectifier (SCR)-incorporated BJT with high holding voltage is developed for electrostatic discharge (ESD) protection in a 0.6 μm high-voltage 10 V process. This device consists simply of a floating P+ diffusion incorporated in a parasitic NPN BJT. A robust 6-7 kV ESD threshold and high-latchup-immune holding voltage of 15-18 V can be achieved by layout optimization of the NPN-N+ -collector to floating P+ -diffusion spacing and the floating P+ diffusion width. It can be equivalently regarded as parallel connection of an incorporated PNPN SCR part and an NPN BJT part. The incorporated SCR part is further composed of a parasitic SCR in series with a reverse-biased PN diode formed by the floating P+ region and N-well. The further analysis shows that the floating P+ diffusion is the key part of this SCR-incorporated BJT. The parasitic reverse-biased PN diode sustains most of the high holding voltage. The parasitic NPN BJT plays a major role in ESD current conduction, while the incorporated SCR in series with the reverse-biased PN diode is the secondary conduction path.