The electron temperature measured by an optical emission intensity ratio of Si* to SiH* in a silane (SiH4) glow-discharge plasma shows an anomalous behavior against film preparation conditions such as gas pressure and substrate temperature. When increasing the gas pressure, the electron temperature decreases first, takes a minimum value at a certain pressure range and then it increases. The electron temperature decreases with increasing substrate temperature, which is quite the opposite trend to a conventional non-reactive hydrogen plasma. These anomalous behaviors of electron temperature in silane plasmas have been explained in terms of feed-back phenomenon in the plasma, starting from an electron-attachment event to higher silane molecules produced in the plasma, causing an increase of electron temperature due to an increase of electron-loss rate, followed by an enhanced production of higher silane molecules. It has also been suggested that the responsible higher silane molecules for the above mentioned feedback phenomenon is penta-silane, Si5H12.