Abstract: This paper presents a hybrid architecture for Spectrum Access Systems (SAS), incorporating permissioned blockchain as a secure, auditable, and interoperable communication infrastructure between different SAS instances. The proposed solution replaces conventional REST interfaces with a distributed layer based on smart contracts, which automates processes such as data-sharing agreements, device registration, and spectrum coordination. The architecture’s feasibility is demonstrated through a functional prototype implemented with Hyperledger Besu, meeting regulatory and operational requirements. Key benefits include data immutability, decentralized governance, and fault resilience, representing a significant advancement in the dynamic and reliable management of spectrum in next-generation mobile networks.