A semiconductor structure includes a first field effect transistor including a first gate spacer having first laterally-straight bottom edges that coincide with top edges of first laterally-straight sidewalls of the first gate dielectric. The semiconductor structure further includes a second field effect transistor including a second gate dielectric that includes at least one discrete gate-dielectric opening that overlies a respective second active region, and a second gate spacer including a contoured portion that overlies and laterally surrounds a second gate electrode, and at least one horizontally-extending portion that overlies the second active region and including at least one discrete gate-spacer openings. The second field effect transistor may have a symmetric or non-symmetric configuration.

In a disclosed Schmitt trigger, an input stage includes a first p-channel field effect transistor (PFET) and a second PFET, which are connected in series to a VDD rail, and a first n-channel field effect transistor (NFET) and a second NFET, which are connected in series between ground and the second PFET. An output stage includes additional FETs for hysteresis. The first PFET and first NFET are different from the other FETs and have a higher voltage rating. For example, the first PFET and first NFET can be buried oxide field effect transistors (BOXFETs) and the other FETs can be laterally diffused metal oxide semiconductor field effect transistors (LDMOSFETs)). Gates of the first PFET and first NFET are connected to an input node. Gates of the second PFET and NFET are connected to receive reference voltages to prevent safe operating area (SOA) violations and control trigger voltage levels.