Scott MacIntyre -- I Need a New Kidney ... Or Music Career Is Kaput

"American Idol" Season 8 finalist Scott MacIntyre says he's got 6 months until his kidney gives out ... and if he doesn't get a new one before then -- his music career is in serious jeopardy.

MacIntyre and his wife were out Saturday night in Hollywood when he told us he's currently waiting for a donor ... but he's hopeful about getting one before his kidney completely fails.

For those interested, Scott told our photog where he's listed ... and said people have already promised him they'd get tested to see if they're a match.

Good luck Scott, we're rooting for you.