  An energy threshold of (220+-10) eV was achieved at an efficiency of 50% with
a four-channel ultra-low-energy germanium detector each with an active mass of
5 g. This provides a unique probe to WIMP dark matter with mass below 10 GeV.
With a data acquisition live time of 0.338 kg-day at the Kuo-Sheng Laboratory,
constraints on WIMPs in the galactic halo were derived. The limits improve over
previous results on both the spin-independent WIMP-nucleon and the
spin-dependent WIMP-neutron cross-sections for WIMP mass between 3-6 GeV.
Sensitivities for full-scale experiments are projected. This detector technique
makes the unexplored sub-keV energy window accessible for new neutrino and dark
matter experiments. Two appendices are included after Version-3 to address
questions raised on trigger and selection efficiencies as well as other issues.
