Hi Harrison,

this sounds just like an application for a VMOS FET device. I do not know
if any of your Drain or source leads will be tied to a fixed potential. If
this is so, look at the HV082 (also called STHV82...and so on) in the
Thomson website. These guys do more than 10 Amps and more than 400 Volts
(but not at the same time...;-).
Another thing to observe: The gate capacitance of such a device is above 1
nanofarad, take care when switching, it needs current to alter the
potential of the gate. The electrode the gate is referenced to is the
Source!
There are some other devices available, their codes begin with IRF....

Greetings, hope this was some help,

Jochen DH6FAZ
jf@detektor.de