\documentclass{standalone}

\usepackage[european,straightvoltages]{circuitikz}

\begin{document}

\begin{circuitikz}
    \draw (0, 0) to [R=$R_1$] (2, 0) to [R=$R_2$] (4, 0) to [R=$R_3$, v<=$U_s$] (6, 0);
\end{circuitikz}

\end{document}
