The kinetics of solid phase epitaxy have been measured in buried amorphous Si layers produced by ion implantation. Crystallization occurs simultaneously at both amorphous/crystalline interfaces of the buried layer. By collecting time resolved reflectivity data simultaneously at &lgr;=1152 nm and &lgr;=632.8 nm it is possible to accurately determine the crystallization rates at both interfaces. Both interfaces crystallize at a constant rate that is comparable to the intrinsic rate found for thick amorphous surface layers before rate retardation due to H infiltration has occurred. Thus, buried amorphous Si layers provide a suitable environment for studies of the intrinsic growth kinetics of amorphous Si. ©1996 American Institute of Physics.