A negative differential resistance with threshold fields of 500, 1200,
and 2000 kV/cm and also a resonant tunneling with a threshold field o
f 1800 kV/cm have been observed in a hexagonal crystal with a natural
6H-SiC superlattice. Analysis of the experimental data shows that thes
e effects can be regarded as manifestations of Wannier-Stark states wi
th various degrees of localization. These results support the position
that Wannier-Stark ''ladders'' exist. This position has come under do
ubt because of the possibility of an interband mixing of electron stat
es by an electric field.