  We present a leptonic model on the external shock context to describe the
high-energy emission of GRB 940217, GRB 941017 and GRB 970217A. We argue that
the emission consists of two components, one with a similar duration of the
burst, and a second, longer-lasting GeV phase lasting hundred of seconds after
the prompt phase. Both components can be described as synchrotron self-Compton
emission from a reverse and forward shock respectively. For the reverse shock,
we analyze the synchrotron self-Compton in the thick-shell case. The calculated
fluxes and break energies are all consistent with the observed values.
