The GameStop investor pushing for changes at the video-game retailer has netted himself a more than $300 million gain in less than six months.

Chewy.com founder Ryan Cohen has snapped up some 9 million shares in the Texas-based chain since last August for an average price of about $8.40 apiece, according to Business Insider.

The value of Cohen’s 13 percent stake has exploded by more than 440 percent thanks to a staggering rally in GameStop’s stock price — fueled partly by last week’s announcement that Cohen had joined the company’s board.

The shares surged another 28 percent on Tuesday to an intraday peak of $45.52, a price that made Cohen’s stake worth nearly $410 million. That gives him a paper profit of about $334 million on his estimated investment of roughly $76 million.

Cohen amassed the bulk of his GameStop stake last August but added another 2.5 million shares in mid-December, Securities and Exchange Commission filings show.

Cohen’s investment firm, RC Ventures, appeared to shore up Wall Street’s confidence in GameStop last week by striking a deal with the retailer to add him and two other former Chewy executives to the company’s board.

The shakeup came on the heels of a strong holiday season that saw GameStop increase its comparable store sales 4.8 percent in November and December, thanks in part to Sony and Microsoft’s release of their latest gaming consoles.