Silicon is a promising alternative to current thermoelectric materials (Bi2Te3). Silicon nanoparticle based materials show especially low thermal conductivities due to their high number of interfaces, which increases the observed phonon scattering. The major obstacle with these materials is maintaining high electrical conductivity. Surface functionalization with phenylacetylene shows an electrical conductivity of 18.1 S m−1 and Seebeck coefficient of 3228.8 μV K−1 as well as maintaining a thermal conductivity of 0.1 W K−1 m−1. This gives a ZT of 0.6 at 300 K which is significant for a bulk silicon based material and is similar to that of other thermoelectric materials such as Mg2Si, PbTe and SiGe alloys.