Absolutely. As PPs have pointed out, this is because of the hormones. I don't think though, that it's been mentioned yet that it's not just the semen that's important here -- it's your enjoyment, which produces oxytocin. Also, the more intense the orgasm, the more it stimulates the uterus. You might also try masturbating while squatting. And even if it doesn't make the labor happen right then, it's still good for the process and helps your body to prepare.
