Big fan of Steph Curry and have half a mil layin' around? Good news -- a super rare SC rookie card has hit the auction block, and it could sell for over $500K!
TMZ Sports has learned ... the 2009 National Treasures autographed patch piece is up for sale at PWCC Marketplace -- and it's such a gem, bidding is already up over $400,000.
The front of the card has a photo of a young Steph in his road Warriors jersey -- and features a cutout of his threads. It also has Curry's autograph in bold, blue ink.
On the back, Curry's stats are displayed ... as well as a nod to one of his most famous triple-doubles.
Officials at PWCC tell us the card is ultra hot right now because it's super rare (it's numbered to just 99) and because Curry -- in addition to already being one of the greatest point guards ever -- is in yet another NBA Finals.
With a series win over the Celtics, Curry would be a four-time champion -- putting him in seriously rare air.
Bidding on the piece ends on June 16 ... best of luck!