Supercritical CO₂ cycles operating with high efficiency require new heat exchangers which can operate at high temperature (above 800°C) and high pressure (above 80 bar) with tens of thousands of hours of operation. In this study, we discuss a modified metallic plate heat exchangers which can withstand high temperature and high pressure with new twisted S-shaped fins. Novel 3D twisted S-shaped fins are developed for higher heat transfer, lower pressure drop, and structural integrity. The fins have a twist to induce a swirl in the flow resulting in enhanced heat transfer. Ni-based superalloy Haynes 214 is the material used for the heat exchanger plates and fins. The heat exchanger is manufactured using additive manufacturing processes. Turbulent Conjugate Heat Transfer simulations are carried out to obtain the temperature and pressure profiles in the heat exchanger. The data from the fluid flow simulations are used to perform the structural simulations to find the thermal expansion and stresses developed in the heat exchanger. The mass flow rates, fin geometry, and plate thickness have varied to identify a suitable design for high temperature and high-pressure applications.