A new electrostatic discharge (ESD) protection device, called quad-silicon controlled rectifier (QSCR), is proposed and verified in a 0.25- μm CMOS process. The QSCR is designed to be used as ESD protection between separated power domains. Since the QSCR embeds four SCRs between its four terminals, no extra ESD clamps are needed to protect the interface circuits between two separated power domains. Implementations with different circuit topologies were also analyzed to achieve a comprehensive ESD protection design for different applications. From the experimental results, the QSCR can withstand 8-kV HBM and 600-V MM ESD stresses with a silicon area of 75 μm ×100μm.