Contents 
We consider Dirichlet problem for a semilinear wave equation with damping term $(\Delta)^\alpha\partial_t u$, where $\alpha\in[0,\frac{1}{2}]$, in a bounded smooth domain $\Omega\subset \Bbb R^3$, assuming initial data from usual energy space $H^1_0(\Omega)\times L^2(\Omega)$. First, we establish control of $L^5([0,T];L^{10}(\Omega))$ norm of solutions for corresponding linear nonautonomous problem in terms of energy norm, which does not follow from energy estimate as well as Strichartz estimates for pure wave equation. Then treating semilinear equation as perturbation of the linear problem we establish its wellposedness in the class of energy solutions with finite $L_{loc}^5(\Bbb R_{+}, L^{10}(\Omega ))$ norm. Moreover, we show that solutions from the mentioned class possess smoothing property analogous to solutions of parabolic equation. Finally we show that dynamical system generated by these solutions possesses a smooth global attractor. 
