Add the marshmallows in one layer on each dehydrator tray. They will puff up so spread them out a little.
Turn the dehydrator on to 120° - 125°. Run for 6 to 12 hours until the marshmallows are hard. The hours will also depend on the dehydrator, humidity, and the size of your marshmallows.
Gently press on the marshmallows to check for firmness. If it still has some give, leave it in the dehydrator for another hour. Check again.
Store in an airtight container or ziplock bag. Press all of the air out of the ziplock bag before sealing it.