In order for URLs to be SEO friendly, they should be clearly named for what they are and contain no spaces, underscores or other characters. You should avoid the use of parameters when possible, as they are make URLs less inviting for users to click or share.
– If your website is new and is not indexed by search engines you can replace underscores with hyphens or redirect those links to URLs that use hyphens.BUT, if your website is ranked well by search engines you do not need to do this (probably you have other ranking factors working very well).
– The general advice remains: build links that contain hyphens rather than underscores and avoid dynamic URLs.
Here’s the Source of this Content