An electrostatic discharge (ESD) protection device coupled across input-output (I/O) and common terminals of a core circuit, comprises, first and second merged bipolar transistors. A base of the first transistor serves as collector of the second transistor and the base of the second transistor serves as collector of the first transistor, the bases having, respectively, first width and second width. A first resistance is coupled between an emitter and base of the first transistor and a second resistance is coupled between an emitter and base of the second transistor. ESD trigger voltage Vtl and holding voltage Vh can be independently optimized by choosing appropriate base widths and resistances. By increasing Vh to approximately equal Vtl, the ESD protection is more robust, especially for applications with narrow design windows, for example, with operating voltage close to the degradation voltage.