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The performance of symmetric double-gate MOSFETs with dopant-segregated Schottky (DSS) source/drain (S/D) regions is investigated through a TCAD modeling study and compared to the performance of raised S/D (RSD) MOSFETs. It is shown that, while the doped extension region adjacent to the S/D Schottky barrier (SB) improves drive current by shrinking the SB, it is fundamentally limited by its dual role as a heavily doped S/D contact region to improve drive current and as a more lightly doped S/D extension region to reduce BTBT leakage. This restricts the design space for meeting low-standby-power leakage specifications, and so, the RSD structure ends up prevailing both in terms of leakage design space and on-state performance. For high-performance (HP) design, where the higher leakage specification permits heavier extension doping, the performances of optimized DSS and RSD MOSFETs are shown to be very similar. Thus, the optimal S/D design for HP is more likely to be decided by practical considerations such as process integration.