http://www.secinfo.com/dr6nd.818y.s.htm#1stPage

http://www.geekwire.com/2011/meet-shel-kaphan-amazoncom-empl...

"So, after five years were up — and my stock was all vested — I probably would have left a little earlier if that had not been the issue.

So, did you hang on to all of the shares because Amazon hit a rough patch just after you left?

“I don’t know what the effect on morale inside the company was since I wasn’t there. But I did do a lot of selling during those times, because from the outside, without knowing what was going on inside the company anymore, I didn’t know if it was going to be a casualty of that era or not, so I cashed out quite a bit of my position. But I did hold on to some of it, and I continue to.”"

Probably between 1 and 2%, I would guess. Some of which he cashed out when the stock was at a low. So between what his current shares are worth now and what he cashed out, probably at least $100 million.

EDIT: His foundation has $53 million in assets, so that should give an idea...

http://990s.foundationcenter.org/990pf_pdf_archive/651/65121...

It was all done on a threadbare budget. At first Bezos backed the company himself with $10,000 in cash, and over the next sixteen months, he would finance the startup with an additional $84,000 in interest-free loans, according to public documents. Kaphan’s contract required him to commit to buying $5,000 of stock upon joining the company. He passed on the option to buy an additional $20,000 in shares, since he was already taking a 50 percent pay cut to work at the startup and would, like Bezos, earn only $64,000 a year. “The whole thing seemed pretty iffy at that stage,” says Kaphan, who some consider an Amazon cofounder. “There wasn’t really anything except for a guy with a barking laugh building desks out of doors in his converted garage, just like he’d seen in my Santa Cruz home office. I was taking a big risk by moving and accepting a low salary and so even though I had some savings, I didn’t feel comfortable committing more than I did.”

(From "The Everything Store")