How do I send a secre request to a php page?

Guys I have to send sensible data to a php page but I'm not too sure if i'm doing it the right way...

for instance:

if I send an ajax request with this URL: 'http://localhost/login.php?username=" & u & "&password=" & p'

to that php page and then I GET the parameters right from the URL, am I passing sensible data in an unsecure way?

Thanks!