Here's the text of the Washington Nationals press release:
The Washington Nationals today promoted right-handed pitcher Stephen Strasburg to Syracuse of the Triple-A International League. Nationals Senior Vice President and General Manager Mike Rizzo and Director of Player Development Doug Harris made the joint announcement.

Strasburg is slated to make his Triple-A debut on Friday, when the Chiefs host the Gwinnett Braves at Alliance Bank Stadium.

The first-overall selection in the 2009 First-Year Player Draft went 3-1 with a 1.64 ERA in five starts with Harrisburg of the Double-A Eastern League. With 27 strikeouts and just six walks in 22.0 innings pitched, Strasburg posted a 4.5/1 strikeout-to-walk ratio and 11.05 strikeouts per 9.0 innings (tops in Eastern League).

Strasburg, 21, ranks among the Eastern League’s top pitchers in several categories: 27 strikeouts (first), 0.86 WHIP (second), 8.18 baserunners per 9.0 innings (second), .165 batting average against (third) and 1.64 ERA (fourth).
This move was expected, as most got wind of the promotion on Staurday, but this makes it official.  Strasburg domninated Double-A and with the step up will get to face more seasoned hitters, a lot with major league experience.

He'll probably get five or six starts with Syracuse before making his debut later at Nationals Park.  Projecting his starts every five days, Strasburg could very well make his major league debut sometime during the June 4-6 series with Cincinnati.  If he remains on his current schedule, he would be in line to pitch Sunday, June 6.

All that is, of course, depending on whether the Nats have the need for a starting pitcher at that point in the season (noted with sarcasm).

See Photo Gallery from Strasburg's last start in Double-A Harrisburg.