Dense ensembles of silicon nanowires were prepared by metal-catalyzed chemical vapor deposition on silicon substrates. Some of these ensembles were doped with phosphorus during growth. The nanowires were characterized using scanning electron microscopy, x-ray diffraction, and mass spectroscopy. Field emission of electrons from these structures was studied at room temperature in ultrahigh vacuum. The measurements were carried out using a parallel-plate diode cell. At high applied fields, the current-voltage characteristics deviate from the Fowler-Nordheim law and exhibit a stepwise increase of the current with increasing voltage at 300K.