  We present results of an ultraviolet photoemission spectroscopy study of
artificially synthesized poly(dA)-poly(dT) DNA molecules on $p$-type Si
substrates. For comparison, we also present the electronic density of states
(DOS) calculated using an \emph{ab initio} tight-binding method based on
density-functional theory (DFT). Good agreement was obtained between experiment
and theory. The spectra of DNA networks on the Si substrate showed that the
Fermi level of the substrate is located in the middle of the band gap of DNA.
The spectra of thick ($\sim 70$ nm) DNA films showed a downward shift of $\sim
2$ eV compared to the network samples.
