Previous calculations show that the two-dimensional (2D) silicon carbide (SiC) honeycomb structure is a structurally stable monolayer.Following this,we investigate the electronic properties of the hydrogen and fluorine functionalized SiC monolayer by first-principles calculations.Our results show that the functionalized monolayer becomes metallic after semi-hydrogenation or semi-fluorination,while the semiconducting properties are obtained by the full functionalization.Compared with the bare SiC monolayer,the band gap of the fully hydrogenated system is increased,in comparison with the decrease of the gap in the fully fluorinated case.As a result,the band gap can be tuned from 0.73 to 4.14eV by the functionalization.In addition to the metal semiconductor transition,hydrogenation and functionalization also realize a direct-indirect semiconducting transition in the 2D SiC monolayer.These results provide theoretical guidance for design of photoelectric devices based on the SiC monolayer.