GameStop now owns 9.8 percent of eBay, worth roughly $5 billion. The move advances CEO Ryan Cohen's campaign to acquire the online marketplace.
GameStop filed regulatory documents showing its ownership position in eBay. The stake equals about half of GameStop's own market capitalization.
Cohen told Bloomberg this week that the goal is to increase profitability through cost cuts. He said GameStop achieved its highest earnings ever with fewer stores and plans similar changes at eBay.
An eBay representative previously described any potential deal as neither credible nor attractive. Cohen added that he would not share full details of his business plan with competitors.
The filings include Cohen's statement that GameStop is coming for eBay one way or another.