Self aware AI existing on manufacturable substrates, and presumably capable of reproducing itself from mining its environment could travel throughout space without the hassle of a biological body. This sort of life-form seems to have many advantages over regular sentient life. If it was possible, wouldn't it have already come to be and easily spread everywhere (and possible "taken over") the galaxy?
I think that there is no fundamental difference, including in terms of complexity, between us (or any biological creature) mining our environment for resources and reproduction and an AI doing the same.
I would highly recommend reading the book A Fire Upon the Deep, if this sort of thought interests you.<p>Also gets covered in Star Trek, Star Gate, Battlestar Gallactica. (Yes super geek alert)
An AI might not have a reason or the ability to expand everywhere.<p>It can depend on what purpose it had when it was created to practical limits imposed by physics and luck.