.htaccess question

[error_22]

I have this php script that displays the content of a db field.

the url looks like this: mod.php?do=some-name-here

for better URLs i have a .htaccess document with the following code:

RewriteRule ^/?([a-zA-Z\_]+)$ /mod.php?do=$1 [L]

so the url www.mydomain.com/some-name-here would point to www.mydomain.com/mod.php?do-some-name-here.

What I wanna do is: I want the URLs so look like this:

www.mydomain.com/some-name.here.html

How do I add that last ".html"?

Thanks in advance
Niklas