The interior of the microwave
is stainless steel. It is not difficult to clean. After use, when it has cooled enough to keep from getting burned, take a damp cloth and wipe it out. If you have cooked something very sticky/gooey/messy on the turntable it may need to be washed in sudsy water. If you have used the rack for broiling, it will need to be washed in sudsy water and perhaps scoured a bit with a steel wool pad.
I have noted on the one that we have in the house that I'm getting some grease buildup. The way I handle this is to microwave some lemon juice then scrub the sides of the microwave with a nylon pot scraper; the grease peels off. I plan to inquire of Sharp if there is a better way to get the grease off.
The bottom line is this: The microwave is not too hard to keep clean. The stainless steel wipes clean pretty nicely. It would be nice if this had a 'self clean' cycle but that'd probably be too much to ask. Maybe Charles'll come by and clean the microwave for me!
Then it'll be Charles-cleaned rather than self cleaning!
Nathan and Daisy