  Let $(X_t)_{t\ge 0}$ be a symmetric strong Markov process generated by
non-local regular Dirichlet form $(D,\D(D))$ as follows \begin{equation*}
\begin{split} &
D(f,g)=\int_{\R^d}\int_{\R^d}\big(f(x)-f(y)\big)\big(g(x)-g(y)\big)
J(x,y)\,dx\,dy, \quad f,g\in \D(D) \end{split} \end{equation*} where $J(x,y)$
is a strictly positive and symmetric measurable function on $\R^d\times \R^d$.
We study the intrinsic hypercontractivity, intrinsic supercontractivity and
intrinsic ultracontractivity for the Feynman-Kac semigroup $$
T^V_t(f)(x)=\Ee^x\left(\exp\Big(-\int_0^tV(X_s)\,ds\Big)f(X_t)\right),\,\,
x\in\R^d, f\in L^2(\R^d;dx).$$ In particular, we prove that for
$$J(x,y)\asymp|x-y|^{-d-\alpha}\I_{\{|x-y|\le 1\}}+e^{-|x-y|}\I_{\{|x-y|>
1\}}$$ with $\alpha \in (0,2)$ and $V(x)=|x|^\lambda$ with $\lambda>0$,
$(T_t^V)_{t\ge 0}$ is intrinsically ultracontractive if and only if
$\lambda>1$; and that for symmetric $\alpha$-stable process $(X_t)_{t\ge0}$
with $\alpha \in (0,2)$ and $V(x)=\log^\lambda(1+|x|)$ with some $\lambda>0$,
$(T_t^V)_{t\ge 0}$ is intrinsically ultracontractive (or intrinsically
supercontractive) if and only if $\lambda>1$, and $(T_t^V)_{t\ge 0}$ is
intrinsically hypercontractive if and only if $\lambda\ge1$. Besides, we also
investigate intrinsic contractivity properties of $(T_t^V)_{t \ge 0}$ for the
case that $\liminf_{|x| \to \infty}V(x)<\infty$.

Probability