Chocolate – the cocoa solids percentage of Hershey’s semi-sweet chips

Milk chocolate is unique in that it contains a significant quantity milk, either in the powdered, liquid, or condensed form.

Dark chocolate is a category of chocolate that includes semisweet and bittersweet chocolate. The US FDA actually does classify dark chocolate as anything containing 35% or more cacao (liquor or butter). In practice, semisweet chocolate is typically much sweeter, and contains about 50% sugar. Bittersweet chocolate, on the other hand, typically contains about 33% sugar. Some dark chocolates may contain small amounts of milk, but not enough to be called milk chocolate.

Source: http://en.wikipedia.org/wiki/Types_of_chocolate

Yes, you can use the choco. chips. One square of chocolate is normally one ounce. Half a cup of chocolate chips is usually around three ounces. If you are looking to use 8 squares (8 ounces), you will need about 1 and a quarter cups of the chips (maybe just a tad more).
Some folks may come on and say that the chips are sweeter, less intense in flavour, etc., but when you are in a pinch, you can sub them out just fine. Doubtful you will notice any difference.