\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}
\usepackage{tikz}
\usetikzlibrary{shapes, calc} 
\tikzstyle{vertex}=[draw,fill=black!15,rectangle,minimum size=20pt,inner sep=10pt]

\begin{document}
\begin{preview}
\begin{tikzpicture}[font=\sffamily,thick,level/.style={sibling distance=120mm/#1}]
    \node[vertex] {Halbleiterspeicher}
        child { 
            node[vertex] {Festwertspeicher}
            child { 
                node[vertex] {Irreversibel} 
                child { node[vertex] {ROM} }
                child { node[vertex] {PROM} }
            }
            child { 
                node[vertex] {Reversibel} 
                child { node[vertex] {EPROM} }
                child { node[vertex] {EEPROM} }
            }
        } child {
            node[vertex] {Schreib- / Lese-Speicher}
            child { node[vertex] {Statisches RAM} }
            child { node[vertex] {Dynamisches RAM} }
        }
    ;
\end{tikzpicture}
\end{preview}
\end{document}
