Low-temperature epitaxy (LTE) of crystalline silicon in the plasma-enhanced chemical vapor deposition (PECVD) was investigated using in situ observation of reflection high energy electron diffraction (RHEED). Source gases of SiH 4 and H 2 mixture were decomposed by radio-frequency (RF) glow discharge, and an epitaxial layer was grown on a p-type Si(001) substrate at a variety of hydrogen dilution ratios, R{([H 2]+[SiH 4])/[SiH 4]}, ranging from 10 to 200, and at substrate temperatures, T s, ranging from 27°C to 560°C. Critical thickness of epitaxy above which polycrystalline growth starts to occur shows two peaks as a function of growth temperature at 120°C and 430°C. The lower temperature peak appeared at 120°C and the surface has a 1×1 structure covered by SiH 2, while at the higher temperature peak of 430°C the surface has a 2×1 (1×2) double domain structure along dimmer rows covered by SiH. In addition, at 430°C, RHEED intensity oscillation with an oscillation period of monolayer was observed. This implies a layer-by-layer growth in the PECVD, and suggests a presence of the surface diffusion of film precursors on the hydrogen-terminated surface. These results are explained in terms of the hydrogen-mediated enhancement of crystal growth corresponding to surface hydride mode.