\documentclass{standalone}
\usepackage{pstricks}
\begin{document}

\begin{pspicture}(-4,-4)(4,4)
\psline[linewidth=1cm](-4,0)(4,0)
\psframe*[opacity=0.5,linecolor=red](-2,-2)(2,2)
\end{pspicture}

\end{document}



