Baking chocolate is usually "semi-sweet" or "unsweetened" chocolate. Many store brand chocolate chips are unsweetened, but some are milk chocolate. If you substitute milk chocolate chips instead of baking chocolate, it may change the taste and melt at a slightly different temperature. If the recipe calls for "unsweetened" chocolate, you may be able to use semi-sweet, but it will have more sugar. A better substitute may be unsweetened cocoa.
- the recipe wikia has several related articles, including one on unsweetened chocolate