No! You can use whatever mix of chocolate you prefer! I love doing 1/2 semi-sweet chocolate chunks (ie a cut up chocolate bar) and 1/2 milk chocolate chips! I think this is the perfect balance of dark vs milk, and pooled vs chips. But, if you are a milk chocolate only type of person, use just milk chocolate! If you only have chips on hand, just use chips. Use whatever you have and whatever you prefer!