Channel recessed 4H-SiC MESFETs were fabricated and have demonstrated excellent small signal characteristics, such as, F-t of 14.5 GHz and F-max of 40 GHz (for MAG = 1). The effect Of Si3N4 passivation on these devices has been studied in this work. Current instability and RF power performance were improved after passivation. From our measurements, we found out that the passivation of SiC NESFETs reduces the surface effects and improves the RF power performance by suppressing the instability in DC characteristics.