parasatic effects in MOSFET?

channel of a mos is the layer formed between the drain and source and is of the same type of that of drain and source

its length is inversely proportional to to the current Id and as it decreases the current increases
in NMOS the applied voltage Vgs increases more negative ions get concentrated in between drain and source which in turn reduces channel length similar thing happens with PMOS
its called channel length modulation effect