Preheat the oven to 350 degrees F ( 175 degrees C).
Place potatoes in a large pot with enough water to cover. Bring to a boil, and cook until potatoes are tender, about 10 minutes. Drain water, and add cream cheese, butter, sour cream and ranch dressing mix. Mash until creamy using a potato masher or electric mixer. Spread evenly in a large baking dish.
Bake for 30 minutes in the preheated oven, until the top is golden brown.