Logic Obfuscation is a well renowned design-for-trust solution to protect an Integrated Circuit (IC) from unauthorized use and illegal overproduction by including key-gates to lock the design. This is particularly necessary for ICs manufactured at untrusted third-party foundries getting exposed to security threats. In the past, several logic obfuscation methodologies have been proposed that are vulnerable to attacks such as the Boolean Satisfiability Attack. Many of these techniques are implemented at the gate level that may involve expensive re-synthesis cycles. In this paper, we present an interconnect obfuscation scheme at the Register-Transfer Level (RTL) using Switch Boxes (SBs) constructed of Polymorphic Transistors. A polymorphic SB can be designed using the same transistor count as its Complementary-Metal-Oxide-Semiconductor based counterpart, thereby no increased area in comparison, but serving as an advantage in having more key-bit combinations for an attacker to correctly identify and unlock each polymorphic SB. Security-aware high-level synthesis algorithms have also been presented to increase RTL interconnects to Functional Units impacting multiple outputs such that when a polymorphic SB is strategically inserted, those outputs would be corrupted upon incorrect key-bit identification. Finally, we run the SMT (Satisfiability Modulo Theories)-based RTL Logic Attack on the obfuscated design to examine its robustness.