  The prompt emission from gamma-ray bursts (GRBs) still requires a physical
explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV
range, show that a hybrid model consisting of two components, a photospheric
and a non-thermal component, in many cases fits bright, single-pulsed bursts as
well as, and in some instances even better than, the Band function. With an
energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented
opportunity to further investigate the nature of the prompt emission. In
particular, it will give us the possibility to determine whether a photospheric
component is the determining feature of the spectrum or not. Here we present a
short study of the ability of GLAST to detect such a photospheric component in
the sub-MeV range for typical bursts, using simulation tools developed within
the GLAST science collaboration.
