  Within the internal shock scenario we consider different mechanisms of high
energy ($>1$ MeV) photon production inside a Gamma Ray Burst (GRB) fireball and
derive the expected high energy photon spectra from individual GRBs during the
prompt phase. The photon spectra of leptonic and hadronic origins are compared
within different sets of parameter regimes. Our results suggest that the high
energy emission is dominated by the leptonic component if fraction of shock
energy carried by electrons is not very small (e.g. $\epsilon_e > 10^{-3}$).
For very small values of $\epsilon_e$ the hadronic emission component could be
comparable to or even exceed the leptonic component in the GeV-TeV regime.
However, in this case a much larger energy budget of the fireball is required
to account for the same level of the observed sub-MeV spectrum. The fireballs
are therefore extremely inefficient in radiation. For a canonical fireball bulk
Lorentz factor (e.g. $\Gamma=400$), emissions above $\sim 10$ GeV are
attenuated by two-photon pair production processes. For a fireball with an even
higher Lorentz factor, the cutoff energy is higher, and emissions of 10 TeV -
PeV due to $\pi^0$-decay can also escape from the internal shocks. The flux
level is however too low to be detected by current TeV detectors, and these
photons also suffer attenuation by external soft photons.
