  We present the measured baseline ionization resolution of a HEMT-based
cryogenic charge amplifier coupled to a CDMS-II detector. The amplifier has
been developed to allow massive semiconductor dark matter detectors to retain
background discrimination at the low recoil energies produced by low-mass
WIMPs. We find a calibrated baseline ionization resolution of $\sigma_E =
91\,\text{eV}_{ee}$. To our knowledge, this is the best direct ionization
resolution achieved with such massive ($\approx$150 pF capacitance) radiation
detectors.
