This paper presents results of selective Si epitaxial growth at 800 °C on (100) silicon wafers with oxide patterns by ultralow‐pressure chemical vapor deposition using pure SiH4 and SiH4/H2. Prior to deposition, the patterned wafers were in situ argon plasma sputtered at -100 V dc bias to remove native oxide. About 800 Å of Si epitaxial layer can be grown selectively on the exposed silicon windows using 3.5 mTorr of SiH4. By flowing H2 with SiH4 during deposition, selective epitaxial layers can be grown to a thickness of 1300 Å before polycrystalline silicon begins to nucleate on the SiO2 surfaces. The epitaxial films were examined by scanning electron microscopy and cross‐sectional transmission electron microscopy and found to be of high structural quality. H2 was found to significantly improve the epi/substrate interface and the surface morphology of the epitaxial layers.