Also, if you can afford some charge injection, or some other means of managing it -- the capacitance will be lower under bias, i.e. high Vds. This is especially pronounced for power MOSFETs, which are not lateral (so not subject to overlap, etc. capacitances familiar to lateral IC MOSFETs), but of vertical and trench designs where the bulk of the substrate itself (or the lightly-doped epitaxy layer on top of it, as the case may be) serves as the off-state capacitor: in particular, SuperJunction trench MOS can have a capacitance ratio of >100:1, with the biggest change in the 10-100V range (depending on rating). The SuperJunction design is... hard to describe, but it has the effect of the capacitance itself practically turning off like a switch, as almost the entire bulk becomes depleted at once (hence the abrupt change in C). Put another way, the thickness of the capacitor suddenly increases from 100s nm, to 10s of um.
Integrated analog switches have a good compromise between on/off ratio; they are specified in terms of insertion loss when on, and attenuation when off, with respect to a given (e.g. 50 ohm) source/load impedance. Capacitances are somewhat irrelevant in that case. Whether this helps you consider your application, I don't know.
Analog switches may internally use tee structures (alternating series/shunt/series switches) to achieve such high ratios. The main downside is probably the limited voltage range, which must be within the supplies; a switch capable of some 100s MHz bandwidth with quite respectable specs, might only be rated for 3.3 or +/-5V. There are fortunately fairly few applications you'd need more (and, when you do, there are proper RF switches to handle that).
If the source/load impedances cannot be well defined (e.g., electrometer input something or other?), a custom solution may be required, or at least ye old fashioned mechanical switches (which offer truly incredible on/off ratios -- do not underestimate them!).
As for the application -- regarding high voltages, if this might be something like mains switching, keep in mind not just the expected (nominal peak) voltage, but also the surge rating, and any characteristics the load might have (inrush current, inductive turn-off). For these reasons, semiconductor applications have largely been confined to only the most robust devices (diodes, SCRs, TRIACs).
Modern devices are just beginning to offer adequate ratings for real power line switching use: SiC MOSFETs with ~kV ratings are adequate to handle surge at low voltages (i.e. 240VAC + 2.5kV surge), but tall stacks of them are needed to also pass the available fault current on such a circuit (~1kA)!
Tim
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