LDMOS n-type transistors are fairly common in power amplifier design. Typically these are done on a silicon process, but you can get ones made on GaAs and GaN (or your preferred flavor).
You may sometimes even find that there are two N-type devices in the single package. This is convenient as it allows for Doherty, balanced or push-pull configurations.
I know Gallium Nitride (GaN) is seeing increasing use in DC-DC converters due to their lower loss and higher breakdown voltages (they are also direct bandgap compared to indirect for silicon). However, they are a pain to control as they are depletion mode devices.