The influence of post-deposition thermal annealing on the thermoelectric properties of n-and p-type nanocrystalline hydrogenated silicon thin films, deposited by plasma enhanced chemical vapour deposition, was studied in this work. The Power Factor of p-type films was improved from 7 x 10(-5) to 4 x 10(-4) W/(m.K-2) as the annealing temperature, under vacuum, increased up to 400 degrees C while for n-type films it has a minor influence. Optimized Seebeck coefficient values of 460 mu V/K and -320 mu V/K were achieved for p- and n-type films, respectively, with crystalline size in the range of 10 nm, leading to remarkable low thermal conductivity values (< 10 W.m(-1).K-1) at room temperature.