escaping wildcard chars

I am trying to pull in the different types allowed by postgres for a create
function statement and am having problems with the types that start with an
underscore (_). Because the underscore is the wildcard for a single
character, I cannot perform the following query correctly.

SELECT typname from pg_type WHERE NOT LIKE '_%'

It gives me an empty set.

Is there any way to escape the underscore. I tried to use '\_%', but that
didn't help. Any suggestions?

-Dan