Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 1 quart baking dish.
In a medium bowl, mix together artichoke hearts, spinach, mayonnaise, Parmesan cheese and 2 cups Monterey Jack cheese. Transfer mixture to the prepared baking dish, and sprinkle with remaining 1/2 cup of Monterey Jack cheese.
Bake in the center of the preheated oven until the cheese is melted, about 15 minutes.