Mention one time to your boss that you believe you're very underpaid. Then, don't say it again. If a raise doesn't come, start looking for a better paying job

Mention one time to your boss that you believe you're very underpaid. Then, don't say it again. If a raise doesn't come, start looking for a better paying job. When you find one, put in your notice, be professional, but don't take the counter offer. It seldom works out.