Hello,
I want to design a back to back MOSFET circuit. If I simplify it, it look like this:

I'd like to know what is the maximum voltage I can apply on bothe transistors. I ask specifically what are the voltages of the transistors I choose. Does the voltage divides evenly when they are both close so I can take a transistor with lower vds?
Thank you.

 

Why do you need this to be bidirectional? What is M2 doing for you? In this circuit M2's internal drain-source diode is forward biassed if M2 is off, so M1 sees -(Vdd - 0.5v) approx Vds.

 

The voltage does not divide evenly, one of them is always acting as a forward biased diode dropping less than a volt.

Bob