He Used to Be

Corey "Big Hoss" Harrison from "Pawn Stars" dropped over 100 POUNDS in less than five months, TMZ has learned -- all thanks to hard work ... and a little help from his doctor.

Hoss tells TMZ, he decided to get lap band surgery back in February -- after his doctor diagnosed him as a prediabetic.

According to Hoss, he's already lost 115 pounds, and continues to shed the weight -- working out with a trainer 5 days a week ALONG with participating in Krav Maga fighting classes.

Hoss' weight issues have been a topic on the show -- and Rick even built a gym in the pawn shop to encourage Hoss and Chumlee to drop the weight.