August Capital has raised $550 million for a new fund, according to August Partner Howard Hartenbaum. The fund, which is the sixth for the Menlo Park-based venture capital firm, includes $300 million for early stage investments and $250 million for “special opportunities” such as growth equity and buyouts. This is the same structure as August’s previous funds.

The firm plans to start investing immediately. Hartenbaum said August has historically done about eight investments per year and expects to maintain a comparable pace moving forward.

Hartenbaum also said the firm is not focused on a particular market segment, citing partner David Hornik’s early investment in Splunk as an example of the company’s investment philosophy to find companies before there is a clearly defined market.

“By the time there’s a well-defined market segment, it’s a little bit late,” Hartenbaum said.

Splunk, a software company that raised its first round from August Capital in 2004, went public earlier this year.

“When [Hornik] funded Splunk in 2004, nobody had ever heard of big data,” Hartenbaum said. “Now, Splunk is the poster child for big data. We are looking for comparably interesting things right now that may not yet have a market segment attached to them.”

August Capital was co-founded in 1995 by David Marquardt, an early investor in and current board member of Microsoft. Recent August investments include PubMatic, SAY Media and WePay. The firm last raised $650 million in March 2009.