The conventional current flowing from the drain to the source is given by

Now, transit time = ( length of the channel) / (electron velocity) = L / v

where velocity is given by the electron mobility and electric field; or,

Now, E_DS = V_DS/ L, so that velocity

Thus, the transit time is

At room temperature (300 K), typical values of the electron and hole mobility are given by

, and

We shall derive the current-voltage relationship separately for the linear (or non-saturated) region and the saturated region of operation.