Graphene exhibits electronic properties that are very sensitive not only to defects but also to the interaction with extra molecules or atoms and underlying substrate. To overcome this limitation for application and mass device production, various methods have been investigated to decouple graphene from substrate and to form quasi-free standing layer. Silicon has shown to be able to softly decouple the zero-layer graphene from the substrate. However, the electronic properties of decoupled zero-layer graphene (ZLG) by silicon intercalation on 6H-SiC(0001) stay unknown. The decoupling process of the ZLG terminated surface happens at lower temperature compared with ZLG covered by 1 monolayer graphene. The presence of extra graphene layer appears to be of an impediment to silicon intercalation. The decoupled ZLG exhibits electronic properties of a quasi-free-standing monolayer graphene. Ab initio calculation corroborates the experimental data and confirms the evolution of the ZLG band structure with silicon intercalation. Copyright © 2014 John Wiley & Sons, Ltd.