Is there a way to set a parbox to a minimum height?

\documentclass{article}

\begin{document}



    \sbox{0}{\parbox{.5\textwidth}{one two three}}
    \ifdim\dimexpr\ht0+\dp0<3cm 
    \dp0\dimexpr3cm-\ht0\fi

    \fbox{\usebox{0}}


\end{document}

This is a bummer:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\tikz\node[draw,minimum height=3cm,text width=0.5\textwidth,inner sep=1pt] {one two three\\four five six};

\end{document}

An alternative solution with tcolorbox package. For unbreakable boxes it's possible to define a height from=height1 to height2 where height1 defines the minimum height to be applied. If text doesn't fill the box it has height1 but if the text is longer, the box uses the needed space.

\documentclass{article}
\usepackage[most]{tcolorbox}
\usepackage{lipsum}

\newtcolorbox{mybox}[1][]{%
    sharp corners, height from=3cm to 20cm, #1
}

\begin{document}

\begin{mybox}
This is a short text
\end{mybox}

\begin{mybox}
\lipsum[1]
\end{mybox}

\end{document}