The effects of surface reconstruction and progressive hydroxylation on the electronic properties of [110] hexagonal silicon nanowires are investigated by ab initio calculations within the density functional theory. Progressive hydroxylation changes the density of states close to valence band maxima and leads to a general decrease in the band gap. The magnitude of band gap reduction is dependent on the facet where the hydroxyl group is bonded. While a high reduction in band gap (10%) is observed for hydroxylation on (111) facets, for (001) facets the reduction is more pronounced (21%) only when there is a (3 x 1) reconstruction. The reduction in band gap is generally accompanied by an off-center radial shift in the location of the charge density arising from the HOMO. These results go to show the impact of surface reconstruction and termination groups on the electronic properties of Si nanowires, which are important for using these materials for biosensor and transistor applications.