The number of M&A deals involving RIAs in the first half of the year fell compared to 2010, but the deal size in terms of acquired assets under management rose significantly, according to Schwab Advisor Services.

There were 27 such deals during the first two quarters, down slightly from 30 for 2010. However, the 27 deals represented some $20.8 billion in acquired assets under management, compared to just $12.4 billion for the same period last year. Accordingly, average deal size in terms of acquired AuM was $770 million this year, compared to $412 million last year.

“Thus far in 2011, we’ve seen a significant leap in the average deal size due to a greater proportion of those with $1 billion or more in AuM, despite a slight decrease in transactions over the same period last year,” said David DeVoe, managing director of strategic business development for Schwab Advisor Services.

A breakdown of the two quarters show deal size increasing over the year: the 12 deals in Q2 represented $13.2 billion in assets under management. The second quarter had an average deal size of $1.1 billion AuM.

“RIAs themselves continue to be the dominant buyer category, demonstrating their growing sophistication in mergers and acquisitions,” said DeVoe. “It also shows RIAs’ willingness to use M&A as one way to achieve business goals and objectives.”

This year’s data was based on updated methodology, and going forward Schwab is focusing its M&A data on firms predominantly serving HNW retail clients; firms with at least $50 million AuM, and breakaway brokers from wirehouses who received consideration for joining an RIA.