  In this paper, we prove a monotonicity formula and some Bernstein type
results for translating solitons of hypersurfaces in $\re^{n+1}$, giving some
conditions under which a trantranslating soliton is a hyperplane. We also show
a gap theorem for the translating soliton of hypersurfaces in $R^{n+k}$,
namely, if the $L^n$ norm of the second fundamental form of the soliton is
small enough, then it is a hyperplane.
