To mitigate the radio-frequency (RF) performance degradation caused by electrostatic discharge (ESD) protection device, low capacitance (low-C) design on ESD protection device is a solution. With the smaller layout area and small parasitic capacitance under the same ESD robustness, silicon-controlled rectifier (SCR) device has been used as an effective on-chip ESD protection device in RF ICs. In this paper, the modified lateral SCR (MLSCR) with the waffle layout structure is studied to minimize the parasitic capacitance and the variation of the parasitic capacitance within ultra-wide band (UWB) frequencies. With the minimized parasitic capacitance, the degradation on RF circuit performance can be reduced. Besides, the fast turn-on design on MLSCR without extra parasitic capacitance from the trigger circuit adding on the I/O pad is also investigated in this work.