By Stephen Nellis and Neha Malara

(Reuters) - Nvidia Corp forecast third-quarter sales above expectations on Wednesday, but results from the data center business of the rising semiconductor industry star disappointed some investors, pressuring shares.

The company, with a market cap that has eclipsed Intel Corp, also beat Wall Street expectations for the second quarter.

Still, the results sent shares down 1.5% in trading after the bell. Before the market close on Wednesday, Nvidia's shares had gained more than 185% over the past year and with a valuation of about 53 times expected earnings over the next 12 months.

Nvidia said it expects third-quarter revenue of $4.40 billion, plus or minus 2%, compared with analysts' estimates of $3.97 billion, according to IBES data from Refinitiv.

The company's data center segment reported second-quarter revenue of $1.75 billion beating estimates of $1.71 billion, according to FactSet data.

Nvidia said Mellanox, the Israeli networking chip firm that it acquired for $7 billion in cash this year, contributed 30% of data center segment sales.

Stacy Rasgon, an analyst with Bernstein, said the figure implied that Nvidia's core data center chips grew only about 6% on a quarterly basis, which may have been lower than some investors with sky-high expectations had hoped.

In an interview with Reuters, Chief Executive and co-founder Jensen Huang said the company is shipping its newest data center products as fast as possible after both introducing them and starting shipments in the second quarter, a process that in the past would play out over several quarters.

"We're going to do a lot more next quarter. We're going to do a lot more the quarter after that," he said. "We're going ramp up here in the second half, and that's going give us another boost."

Nvidia's gaming business posted revenue of $1.65 billion, beating FactSet estimates of $1.41 billion.

Revenue rose nearly 50% to $3.87 billion in the second quarter ended July 26, Nvidia said, above Refinitiv IBES estimates of $3.65 billion.

Net income rose to $622 million, or $0.99 per share, in the quarter, from $552 million, or $0.90 per share, a year earlier.

On an adjusted basis, the company earned $2.18 per share in the quarter compared with analysts' estimates of $1.97 per share.

Nvidia was once primarily known for chips that helped video game graphics look more realistic. But more than a decade ago, Huang placed a major bet on the rise of artificial intelligence applications such as the image recognition or natural language processing computing that powers everything from autonomous vehicle development to voice assistants.