Volkswagen priced Porsche AG shares at the top end of the indicated range and raised 19.5 billion euros from the flotation to fund the group's electrification drive.
Porsche AG stock was trading up 3% from the issue price of 82.50 euros at 1035 GMT.
That lifted Porsche AG's valuation to 77.4 billion euros, close to the market capitalisation of Volkswagen as a whole, which is worth around 80.1 billion euros, and puts it ahead of rivals like Ferrari (RACE.MI).
Shares in Volkswagen and holding firm Porsche SE (PSHG_p.DE), which owns a blocking minority in Porsche AG, were down 4.6% and 8%, respectively, as investors switched across.
Up to 113,875,000 preferred Porsche AG shares, carrying no voting rights, were sold in the initial public offering.