Preheat oven to 350 degrees F. In a large bowl, mix together cream of chicken soup, sour cream, corn, Ro-tel, chicken and 2 cups of pepper jack cheese. Spread into an 8x8 or 9x9 baking pan. Set on top of a baking sheet to prevent spills in your oven.
Sprinkle remaining cup of pepper jack onto the casserole. Spread the crushed Doritos evenly over the cheese. Cover with foil and bake for 25 minutes. Remove foil and bake another 15 minutes.