Currently, SiC is widely recognized as one of the most prominent wide bandgap semiconductors, with expanding applications in harsh environments, such as high temperature and radiation exposure. We developed a planar structure 4H-SiC GAA JFET, where the channel region is formed through ion implantation at varying doses, and its transfer characteristics were evaluated. Moreover, we constructed a common-source amplifier and assessed the maximum voltage gain. We were able to modify the threshold voltage and produce both normally-on and normally-off JFETs by changing the amounts of channel dose. The maximum voltage gain of SiC GAA JFET source-common amplifier is estimated to be −17.1 (24.6 dB), −112.6 (41.0 dB), and −226.7 (47.1 dB) at VDD=10, 20, and 30 V, respectively.