The drain conductance of n-channel MOSFET in linear region is:

If VDS < VGS - VT

Then MOSFET is in the active region (linear region)

Drain current is given by

If VDS ≥ VGS - VT

The mode of operation is saturation in the region.

For trans-conductance, we differentiate drain current w.r.t. VGS

In the active region (Linear region)

So, drain conductance of n-channel MOSFET in the linear region
= 

Additional Information

In saturation region