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A stacked-NMOS triggered silicon-controlled rectifier (SNTSCR) is proposed as the electrostatic discharge (ESD) clamp device to protect the mixed-voltage I/O buffers of CMOS ICs. This SNTSCR device is fully compatible to general CMOS processes without using a thick gate oxide to overcome the gate-oxide reliability issue. ESD robustness of the proposed SNTSCR device with different layout parameters has been investigated in a 0.35 /spl mu/m CMOS process. The HBM ESD level of the mixed-voltage I/O buffer with the stacked-NMOS channel width of 120 /spl mu/m can be obviously improved from the original /spl sim/2 kV to be greater than 8 kV by this SNTSCR device with device dimensions of only 60 /spl mu/m/0.35 /spl mu/m.