Electrostatic discharge (ESD) protection is a must in every integrated circuit. It is done by deploying a network of special devices on-chip, alongside the functional elements. The demand for continuously improvements in ESD design and simulations brings the need of new and more accurate scalable models. The SCR (silicon controlled rectifier) is one of the most efficient ESD protection devices. A new electrical model, that can be used to evaluate the complex protection structures of which it is part of, was developed during this thesis. Built with a strong relation between the physical phenomena and its equations, it was rendered scalable, offering the possibility of tailoring and optimizing the device according to the needed protection level. Moreover, a high-frequency study on the SCR and the ESD protection diode was carried out, leading to a model able to predict the impact these devices have on the protected circuit.