Monolithic SiB4±x and SIB6 plates about 1 nm in thickness were prepared by CVD using SiCl4, B2H6 and H2 gases as source materials. The CVD-SiB4±x, plates have nonstoichiometric compositions between B/Si=3.1 and 5.0. The lattice parameters of the CVD-SiB4±x, plates are a=0.633 nm and c=1.262 to 1.271 nm. The density of the CVD-SiB4±x ranges from 2.39 to 2.45 g/cm3. The CVD-SiB6 plates have a constant composition of B/Si=6.0. The lattice parameters of the CVD-SiB6plates are a=1.444 nm, b=1.828 nm, c=0.9915 nm, and their density Is 2.42 g/cm3. These measured densities are both almost in agreement with theoretical values. The electrical conductivity, Seebeck coefficient, Hall mobility and thermal conductivity of the CVD-SiB4±x and CVD-SiB6 plates were examined in the temperature range from 300 to 1000K. The conduction mechanism Is discussed and their figure of merit values for thermoelectric materials are evaluated.