Drain current as a function of temperature
The drain current depends on carrier mobility (which decreases with increasing temperature by about -0.3 %/deg C); carrier concentration (which increases negligible with temperature), and threshold voltage (which decrease with temperature by about -2 mV/deg. C).

At gate voltages just above the threshold voltage (say &lt; 500 mV above), the threshold variation dominates, and drain current increases with temperature. Conversely, at significantly higher gate voltages (say more than 1 V above threshold), the mobility term dominates, and drain current decreases with temperature.