A core-shell nanofin vertical switch performs high-voltage switching and includes: an n-type GaN nanofin core including: an n-type drift layer; an n-type channel; and an n-type source; a p-type nanofin shell surrounding the n-type GaN nanofin core at an interface surface of the n-type GaN nanofin core, and comprising GaN; an optional source contact disposed on the n-type GaN nanofin core and the p-type nanofin shell and in electrical communication with the n-type source, such that the n-type source is interposed between the source contact and the n-type channel; and a gate contact disposed on the p-type nanofin shell and in electrical communication with the p-type nanofin shell, such that the p-type nanofin shell is interposed between the gate contact and the n-type channel, and the gate contact is interposed between the source contact and a drain contact.