[jhpankow]

Is it possible that your "Structure of an inverter" image is mislabed? NMOS would be on the left and PMOS on the right. My thinking is the PMOS has the extra diffusion step to create the n-well for the channel under the gate.

[kens]

It's quite possible that they are reversed; I'm sort of guessing. PMOS transistors are usually bigger, so I think it's the one on the left. The chip could have n-wells or p-wells, so it could go either way with the extra diffusion.