Room-temperature selective Si growth is possible by irradiating an electron beam on a Si surface in a Si2H6 ambient. The growth has an apparent substrate temperature dependence, such that the selective growth of Si is allowed at substrate temperatures only below 330 degrees C. We have found by the H-2 thermal desorption experiments that the Si surface during the growth is covered with higher Si hydrides such as: SiH2, SiH3, and Si2H6 molecules. This indicates that the selective Si growth is caused by the higher Si hydrides. The reaction schemes of the Si growth are discussed in this article.