Convert WP Menu to a Drop Down for Mobile browser

Question

I'm working on a wp project with responsive theme.

I have single level nav menu at the top of the site, that I want to change to a Select Option tag for mobile browsers (small screens) with options for the nav items which is much easier to select in mobile site. So the UL LI menu will be replaced with a Selection- Option tag for mobile.

However, I'm unable to figure out how to change wp menu to a select option dropdown.