  We present data for 18 blazars observed with ASCA, half of which were also
observed contemporaneously with EGRET as parts of multi-wavelength campaigns.
The observations show a clear difference in the spectra between three
subclasses of blazars, namely the High-energy peaked BL Lac objects (HBLs),
Low-energy peaked BL Lac objects (LBLs), and quasar-hosted blazars (QHBs). We
find that the radiation process responsible for the HE peak for HBLs can be
explained solely by Synchrotron-Self-Compton (SSC) emission, with the Doppler
factor consistent with the VLBI and/or gamma-ray variability data. For many
QHBs, on the other hand, the gamma-rays cannot be solely due to the SSC
mechanism unless the Doppler factor is significantly in excess of that inferred
from VLBI data. We consider an alternative scenario consistent with the
measured values of the Doppler factor, where the SSC component is still present
in QHBs and it dominates in the X-ray band, but it is below the observed
gamma-ray spectrum. With an assumption that the peak of the SSC emission is on
the extrapolation of the X-ray spectrum, and adopting the Doppler factor of 10,
we infer the magnetic field to be 0.1 - 1 Gauss, and Lorentz factors of
electrons radiating at the peak of the nu F(nu) spectrum of 10^3 for QHBs; this
is much lower than 10^5 for HBLs. This difference is most likely due to the
large photon density expected in QHBs.
