  In this paper, we investigate the global behaviors of solutions to defocusing
semilinear wave equations in $\mathbb{R}^{1+d}$ with $d\geq 3$. We prove that
in the energy space the solution verifies the integrated local energy decay
estimates for the full range of energy subcritical and critical power. For the
case when $p>1+\frac{2}{d-1}$, we derive a uniform weighted energy bound for
the solution as well as inverse polynomial decay of the energy flux through
hypersurfaces away from the light cone. As a consequence, the solution scatters
in the energy space and in the critical Sobolev space for $p$ with an improved
lower bound. This in particular extends the existing scattering results to
higher dimensions without spherical symmetry.
