  We present an experimental study of low temperature electronic transport in
the hybridization gap of inverted InAs/GaSb composite quantum wells.
Electrostatic gate is used to push the Fermi level into the gap regime, where
the conductance as a function of sample length and width is measured. Our
analysis shows strong evidence for the existence of helical edge modes proposed
by Liu et al [Phys. Rev. Lett., 100, 236601 (2008)]. Edge modes persist inspite
of sizable bulk conduction and show only a weak magnetic field dependence - a
direct consequence of gap opening away from zone center.
