We realize that some students, especially in the humanities, prepare books related to their theses or dissertations. In general, it appears to be the case that electronic release of early versions of a book leads to greater sales of such books. Indeed, having an electronic work made available on the Internet, and telling a publisher that there have been a large number of electronic accesses to that work, may help you land a book contract.
Usually, books that relate to theses or dissertations turn out to be significantly different because they are revised as part of the editorial process. This makes it likely that those interested in your work will buy your book when it comes out, even if they have reviewed your thesis/dissertation.
However, since publishers vary widely in their policies, you should confer with publishers to which you are likely to submit your work prior to final submission.