In this paper, we present recent results on an SiC MESFET and we describe two of the main limitation mechanisms encountered: the self-heating and the trapping effects. Results on recent MESFET devices processed by THALES Research and Technology (TRT), Colombes, France, show that the trapping effects has been solved by using epitaxial layers on a higher purity 4H-SiC semi-insulating substrate sample made with a new technique by Okmetic, Vantaa, Finland. The association of two chips in the same case showed that the main limitation mechanism for power density originates from self-heating effects, which could be solved by optimizing the chip layout. 37.8-W output power at 500 MHz, 1.78-W/mm power density, and 35-dB third-order intermodulation-distortion ratio are the best obtained performances. An experimental analysis of trapping and self-heating effects on large-periphery SiC MESFETs is proposed in this paper.