Aspects relate to mechanisms for sidelink reservation across frequency bands. In some examples, a sidelink device may be configured to communicate over a first frequency band (e.g., a sub-6 gigahertz frequency band) and a second frequency band (e.g., a millimeter wave frequency band) with one or more other sidelink devices. The sidelink device may further be configured to perform cross-link resource reservation for a sidelink transmission in which a resource reservation message transmitted on the first frequency band indicates reserved resources within the second frequency band for the sidelink transmission. The sidelink device may then transmit sidelink control information (SCI) within a sidelink control channel on the second frequency band and user data traffic corresponding to the SCI within a sidelink data channel on the second frequency band.