The median home price in Southern California last month rose 22.5 percent from a year earlier and topped $300,000 for the first time in 20 months, as sales continued shifting from low-priced inland areas to higher-end coastal regions, a tracking firm reported Tuesday.

San Diego-based MDA DataQuick reported that last month's median of $305,000 in the six-county region was up from $249,000 in May 2009 and up 7 percent from $285,000 in April.

The May median, which marked a sixth consecutive month of year-over-year increases, was at its highest level since October 2008, DataQuick said.

"Last month's jump in the regional median sale price is the flip side of what we saw a year ago, when low-cost inland foreclosures dominated and sales in the costlier coastal towns struggled for a pulse," DataQuick President John Walsh said.

Sales last month of homes costing $500,000 or more made up 21.6 percent of all transactions in the region, up from 17.4 percent a year ago, DataQuick said.

Foreclosures, meanwhile, which typically account for the lowest-price homes, comprised 33.9 percent of resales last month, down from 49.8 percent a year ago, the firm said.

"Today the bargains on foreclosures are fewer and farther between, and the high end is approaching a normal sales rate," Walsh said.

DataQuick also said home sales increased 7.2 percent in May to 22,720, resuming a trend of year-over-year increases that was broken in April when sales dropped for the first time in nearly two years. May's sales were the highest for that month since 2006.

Walsh cautioned that much of May's activity was fueled by the availability of a federal tax credit for first-time home buyers that is in the process of being phased out.

He said it remained to be seen how the market would respond to the withdrawal of the credit and other government interventions, such as those keeping mortgage rates low.

"What we saw in May was partly driven by government stimulus," he said. "In the second half of the year, the market will have to stand on its own again."