Sirius Satellite Radio‘s Web site received hits from 1.9 million unique visitors in March, up from 666,000 unique visitors in March 2005, an increase of 188 percent, according to Nielsen//Netratings, an Internet media and market research firm.

XM Satellite Radio also saw strong year-over-year growth, climbing 47 percent from 1.2 million unique visitors in March 2005 to 1.7 million in the most recent month. However, Sirius site traffic has surpassed that of rival XM throughout the first three months of 2006, coinciding with Howard Stern’s long-awaited debut on Sirius.

“The satellite radio market is enjoying vibrant growth, due to increasing interest among first time subscribers,” Jon Gibs, senior director of media, Nielsen//Netratings, said in a statement. “While Sirius has seen significant growth specifically due to Howard Stern’s programming, both services benefit from individuals going to their site, not just to sign up for service, but also to listen to content while they are without their players.”

Since the beginning of 2006, Sirius has recorded 5.8 million unique visitors to its Web site, while XM has had 4.9 million unique visitors.