You should increment only the MINOR version number, assuming that the new features are backward compatible.
Rationale:
semver 2.0.0 makes this crystal clear in clause 7:
- Minor version Y (x.Y.z | x > 0) MUST be incremented if new, backwards compatible functionality is introduced to the public API. It MUST be incremented if any public API functionality is marked as deprecated. It MAY be incremented if substantial new functionality or improvements are introduced within the private code. It MAY include patch level changes. Patch version MUST be reset to 0 when minor version is incremented.