dude......itz does depend on sizes .
the threshold voltage changes with the ratio Wp/Wn.The reason for this is that the more mobile electrons in the
NMOSFET enable the NMOSFET to operate at a lower VDS than the PMOSFET for the same
IDS, hence pulling VOUT (= VIN at threshold) low. The threshold voltage can be increased by
increasing the width of the PMOSFET (hence Wp/Wn) so that the VDS of the PMOSFET falls.
In fact, if the ratio Wp/Wn = μn/μp = 2.7, then a threshold voltage of VDD/2 is achieved