We have studied the interaction of SiH4 with Si(100)2x1 and with Si(111)7x7 utilizing scanning tunneling microscopy. At 690 K Si deposition does not saturate, but the reactive sticking coefficient is considerably larger for Si(100)2x1. On this surface the 2x1 reconstruction is preserved during deposition. The anisotropy of the newly formed islands and the growth process are influenced by the presence of hydrogen from dissociated SiH4. In contrast, the Si(111)7x7 surface is completely restructured by the interaction with SiH4. This results in the formation of a bulklike hydrogen terminated 1x1 structure without any remnants of stacking faults. After exposure to 50 000 L SiH4 at 690 K not more than half a bilayer has grown, forming triangular Si(111)1x1-H islands.