While the answer has already been given, I think it's important for people to understand certain details.
The Dominican constitution recognizes both, jus sanguinis (citizenship by blood) and jus solis (citizenship by birth.)
While many people think that Dominicans born to at least one Dominican parent in the DR gains citizenship via jus solis and those born abroad via jus sanguinis, in reality 100% of ethnic Dominicans (all that is required to be an ethnic Dominican is to have at least one Dominican parent) inherits Dominican citizenship exclusively through jus sanguinis. That's true for island born as well as those born overseas.
The recognition of jus solis exist as a way to 'reward' foreign couples with legal residency in the DR, as such their kids gain Dominican citizenship simply for being born on Dominican soil. However, from that generation forward Dominican citizenship is actually acquired via jus sanguinis, not jus solis, regardless if their offsprings are born on the island or abroad.
Notice that foreign couples with illegal residency in the DR are not able to produce a Dominican citizen simply by birth. Dominican jurisprudence is designed in such a way that an illegality can't produce legal rights. In order for a legal right to be conferred, the original illegality (lets call it the original sin) must be rectified and then, and only then, it automatically rectifies the situation of the entire descendancy starting with the original illegal foreign couple that legalizes their situation. Believe it or not, the legalization can even be done well after the original illegal foreign couple dies, given that the proper legally established procedures are followed through. The easiest way to void the lets call it inherited mark of the original sin is if the offsprings of the illegal foreign couple have children with Dominican citizens, because Dominican law never negates Dominican citizenship to the son/daughter of any Dominican. Again, every ethnic Dominican gains citizenship via jus sanguinis.
Believe it or not, this very simply and straightforward concept is too complicated (perhaps too abstract) for many people to understand. Don't ask me why, because I don't know why some people don't get it regardless how many ways you try to explain it to them, especially the part that fixing the original illegality automatically fixes the situation for the entire line of descent. So if you try to explain this to someone and they don't get it, just give up. It isn't worth it to break your head open for someone that simply doesn't get it.