In recent years, THz spectral range has gathered attention due to its applications in various fields like sensing, microscopy, optical communication, defence, and bio-photonics. Accompanied by field confinement effects offered by metal nanostructures and optical nonlinear response, THz range has become even more promising. The highly confined nature of electromagnetic fields within a nano-slit antenna have high potential in enhancing light-matter interactions and device miniaturization. Under intense laser illumination, the THz response of nano-slit antenna exhibits nonlinear behaviour, particularly in hybrid systems involving metal–semiconductor interfaces. The nonlinear response involves alteration in carrier mobility as well as intensity dependent transmission. Such hybrid structures may find applications in development of efficient THz sources, detectors and devices. In this Chapter, we present recent works done towards the demonstration of nonlinear effects in THz range aided by extreme field confinement within a nano-slit antenna.