  At the end of inflation the universe is frozen in a near zero-entropy state
with energy density in a coherent scalar field and must be ``defrosted'' to
produce the observed entropy and baryon number. We propose that the baryon
asymmetry is generated by the decay of supermassive Grand Unified Theory (GUT)
bosons produced non-thermally in a preheating phase after inflation. We show
that baryogenesis is possible for an inflaton masses of order 10^{13} GeV and a
GUT Higgs boson mass of order 10^{14} GeV, thus solving many drawbacks facing
GUT baryogenesis in the old reheating scenario.
