iPhone lust is growing sharply among American teenagers, according to a note to clients issued Monday by Piper Jaffray’s Gene Munster.

Summarizing the Apple (AAPL) portion of PJC’s semi-annual survey of teen buying habits, Munster reported that “Apple’s dominance in the [consumer electronics] and online music markets is going seemingly unchecked.”

Specifically:

• 31% of the U.S. teens surveyed planned to buy an iPhone in the next six months, up from 22% last fall and nearly double the 16% who wanted one a year ago.
• 14% already own an iPhone, up from 8% a year ago, but down a point from 15% six months ago.
• Of the 87% who own an MP3 player, 92% own an iPod. Of Apple’s major competitors, only Microsoft (MSFT), Sony (SNE) and Sandisk (SNDK) showed up in the results, with 3% market share each.
• Of the 82% of teens who download music, 43% do it legally. Of those, 92% get their music from Apple’s iTunes Store.

“We believe that the teen demographic is a critical component of long-term growth in the digital music and mobile markets,” wrote Munster. “And Apple is taking its leading position in music and mobile markets.”

Piper Jaffray’s 19th semi-annual teen survey questioned 6,000 students across the U.S., 261 of whom completed the Apple-related portion of the survey.

See also:

• Survey: 22% of U.S. teens want an iPhone; 15% already own one
• 16% of teens, 30% of professionals plan to buy iPhones
• Survey: 8% of U.S. teens own an iPhone; 22% want one
• Survey: 6 percent of U.S. teens own iPhones
• Report: 3% of U.S. Teens Surveyed Already Own iPhones

[Follow Philip Elmer-DeWitt on Twitter @philiped]