The future of mobile computing may be… e-Readers? Yes, even though iPads and other tablets are more attractive and more multifunctional, they’re also far less successful than e-Readers in the U.S., with 12% of Americans owning an e-Reader against only 8% owning a tablet device. And again bucking conventional wisdom, the gap is widening.

A new study from the Pew Research Institute points out that the share of adults in the U.S. who own an e-Reader device doubled from 6% to 12% in the six months since November 2010, with growth for tablet users far slower, going from 5% in November 2010 to 8% in April/May 2011.

The study also showed that 3% of Americans own both a tablet and an e-Reader, presumably because they can’t help themselves from buying devices even if their functionality is duplicated.

The largest growth demographics for e-Readers over the last six months may also be surprising: Hispanic adults, parents of young children and households of an income above $75,000 a year made the biggest gains, with men slightly more likely to purchase the devices than women.

Interestingly enough, the same – minus the parenting – is true of tablet growth. Clearly, Hispanic men making more than $75,000 are the new target market of mobile computing companies. Apple, take note.

MORE: Should You Buy an eBook Reader?