We present the first study of ultrafast hole dynamics after resonant inters
ubband excitation in a quasi-two-dimensional semiconductor. p-type Si0.5Ge0
.5/Si multiple quantum wells are studied in pump-probe experiments with 150
fs midinfrared pulses. Intersubband scattering from the second heavy-hole
back to the first heavy-hole subband occurs with a time constant of 250 fs,
followed by intrasubband carrier heating within 1 ps. Such processes give
rise to a strong reshaping of the intersubband absorption line, which is ac
counted for by calculations of the subband structure, optical spectra, and
hole-phonon scattering rates.