\useasboundingbox (-1,-0.5) rectangle (6.25,6);

\node[anchor=north] at (0,0) {0};
\draw[thin] (0,0) -- (0,-0.075);
\node[anchor=east] at (0,0.25) {0};
\draw[thin] (0,0.25) -- (-0.075,0.25);

\draw[{Latex[round,scale=1.2]}-{Latex[round,scale=1.2]},thick] 
  (0,5.75) -- (0,0) -- (6,0);

\draw[thick] (0,0.25) -- (1.5,0.25);

\draw[gray] plot[smooth,domain=2.75:4.25] 
  (\x, {1.4*(\x-3.5)+1.65});

\draw[gray] (3, 0.95) -- (4, 0.95) -- (4, 2.35);

\draw[{Latex[round,scale=0.6]}-] (3.5,0.95) --++ (0,-0.3) 
  node[ anchor=north
      , font=\scriptsize
      , inner sep=2pt
      ] {$\Delta V$};

\draw[{Latex[round,scale=0.6]}-] (4,1.65) --++ (0.3,0) 
  node[ anchor=west
      , font=\scriptsize
      , inner sep=2pt
      ] {$\Delta I$};

\node[] at (2,3.5) 
  {$g_{\mathrm{m}} = \frac{\Delta I}{\Delta V}$};

\draw[thick] plot[smooth,domain=1.5:5] (\x, {0.7*0.5*(\x-1.5)^2+0.25});

\filldraw (3.5, 1.65) circle (1pt);

\node[anchor=south] at (6,0) {$V_{\mathrm{GS}}$};
\node[anchor=east] at (0,5.75) {$I_{\mathrm{D}}$};