Filament temperature is an important parameter in the hot-wire chemical vapor deposition (HW-CVD) process, affecting both the growth rate and electronic properties of the deposited thin films. Here we describe direct detection of gaseous free radicals produced as a function of filament temperature in the HW-CVD of amorphous silicon from silane. Radicals have been identified using vacuum ultraviolet (VUV) single photon ionization (SPI), with 118-nm light formed by the 9th harmonic of a Nd:YAG laser. The major silicon-containing gas-phase species identified by SPI during hot-wire activation of silane gas are Si, SiH3 and Si2H6. At the lower filament temperatures (900-1300 degreesC) studied, consumption of silane is observed without significant formation of Si-containing radicals. The concentration of Si rises rapidly with filament temperature near T-til = 1300 degreesC before leveling off at temperatures above 1800 degreesC, while SiH3 and Si2H6 concentrations become significant only at the highest temperatures.