\node[nmos](m1) at (0,0) {};

\draw (m1.gate) to [short,- ] (m1.gate|-m1.drain)
                to [short,-*] (m1.drain)
                to [ american current source
                   , l=$I_{\mathrm{0}}$
                   , invert
                   ] ++ (0,2)
                node[vdd] {};

\node[vss] at (m1.source) {};

\path [voltarrow] ($(m1.drain)+(0.15,0)$) edge[bend left=20] 
    node[midway,right,font=\small,inner sep=2pt] 
    {$V_{\mathrm{DS}}$} ($(m1.source)+(0.15,0)$);
\path [voltarrow] ($(m1.gate)+(-0.05,-0.05)$) edge[bend left=-20] 
    node[midway,left,font=\small,inner sep=2pt] 
    {$V_{\mathrm{GS}}$} ($(m1.source)+(-0.025,-0.1)$);