4H-SiC planar MESFETs having submicron-gate length were fabricated using ion-implantation and their DC and RF performances were characterized. The ion-implantation process which is essential to fabricate a planar device was investigated. Activation annealing after ion-implantation was performed in induction heating system under Ar atmosphere and the annealing condition was optimized. The fabricated MESFET showed good contact properties and pinch-off characteristics. The possibility of application of planar MESFETs in high voltage operation was suggested.