Aug 23 (Reuters) - On Holding AG, a shoe firm backed by Swiss tennis star Roger Federer, on Monday filed for an initial public offering in the United States and revealed its net sales had jumped 85% in the six months ended June 30. The company was valued at nearly $2 billion after its last funding round, Reuters reported in April. Federer had invested in On in 2019, according to the filing. It was not immediately known how much the Swiss tennis star has invested in the shoe firm. The 20-times Grand Slam winner had also teamed up with the company earlier this year to develop the Roger Pro tennis shoe. U.S. venture capital firm Stripes holds 12.4% of the company"s ordinary shares, the filing showed. On said it had not set the terms for its offering yet. Sources told Reuters in April that the company could seek a valuation of between $4 billion and $6 billion in its IPO. For the six months ended June 30, net sales jumped to 315.5 million Swiss francs ($344.01 million) from 170.9 million Swiss francs a year earlier, the company said. It also reported a net income of 3.8 million Swiss francs, compared to a loss of 33.1 million Swiss francs a year earlier. Running-shoe makers have seen sales spike in the COVID-19 pandemic as people turn to running, with gyms closed and team sport activities banned. On was founded in 2010 in Zürich, Switzerland by Olivier Bernhard, David Allemann and Caspar Coppetti. Goldman Sachs & Co, Morgan Stanley and J.P. Morgan are among the underwriters for the offering. The company said it would be listed on the New York Stock Exchange under the ticker symbol "ONON". ($1 = 0.9147 Swiss Francs)