C-MESFETs often suffer from low breakdown voltage, limited output power, and reduced RF efficiency. We pro pose a TOx-MESFET that reshapes device electrostatics by shifting the gate toward the source, inserting an oxide at the gate edge, and embedding a tungsten layer above the buried oxide while isolating it from the semiconductor with a thin Si3N4 interlayer. This structure redistributes the electric field, suppresses crowding at the gate-drain side, and maintains a wider effective channel under bias, improving both DC robustness and high-frequency per formance. Simulations show that breakdown voltage rises from 15.8 to 39.69 V, saturation drain current from 0.168 to 0.182 A/mm, and maximum output power from 0.300 to 0.858 W/mm. RF metrics also improve: 𝐹𝑇 increases from 19.3 to 25.5 GHz, 𝐹max from 80 to 108.18 GHz, current gain from 56.6 to 84.5 dB, MTG from 34.25 to 48.8 dB, GMS from 124 to 170 dB, and 𝑈 from 15 to 19.45 dB.
