The electronic structure of hydrogenated amorphous silicon layers is calculated within the empirical tight binding approximation. We predict an important blueshift due to the confinement for layer thickness below 3 nm, and we compare with crystalline silicon layers. The radiative recombination rate is enhanced by the disorder and the confinement but remains much weaker than that in direct band gap semiconductors. The comparison of our results with experimental data shows that the density of defects and localized states in the studied samples is quite small. ©1997 American Institute of Physics.