Semi-sweet and dark chocolate are essentially the same thing... there are varying "degrees" of darkness, which will depend on the brand you choose.
As far as using chocolate chips instead of baking squares, an article I read says, "the mistake made most frequently by inexperienced bakers is using semi-sweet chocolate morsels when the recipe actually calls for semi-sweet chocolate. Morsels were developed not to melt in the oven in cookies, so don't use those."
I think it just depends on your recipe, as to how well the chips would work. I would probably stick to the recipe, but if you use the chips, let us know how it turns out!