A method of determining one or more transistors within a particular circuit to be respectively replaced with a hardened transistor includes: identifying, as not requiring hardening, one or more transistors; identifying, as candidates for hardening, each transistor in the circuit not previously identified as not requiring hardening; and employing the hardened transistor in place of a transistor identified as a candidate for hardening. The circuit is a latch and the transistor is an SOI CMOS FET. The transistor is also an SOI transistor. The series transistor includes first and second series-connected transistors having a shared source/drain region whereby a drain of the first series-connected transistor is merged with a source of the second series-connected transistor.