  We investigate the synchrotron self-Compton process in a planar shell taking
the shock structure into account. We find that the energy density of the seed
photons could deviate from the one-zone estimate by order of unity depending on
the shock velocity and the electron cooling time. We also find that as the
electron cooling becomes faster, the seed photons are increased more, so that
the inverse Compton cooling becomes more efficient. This ``ultra'' fast cooling
may work in such as gamma-ray bursts, blazars and microquasars.
