  We study Dirac-Born-Infeld (DBI) inflation models with multiple scalar
fields. We show that the adiabatic and entropy modes propagate with a common
effective sound speed and are thus amplified at the sound horizon crossing. In
the small sound speed limit, we find that the amplitude of the entropy modes is
much higher than that of the adiabatic modes. We show that this could strongly
affect the observable curvature power spectrum as well as the amplitude of
non-Gaussianities, although their shape remains as in the single-field DBI
case.
