Since going on sale in Japan last December, there have been 31 incidents in which the PS Vita overheated, rendering the machines inoperable. As of early June, 23 of those incidents were in Japan, while 8 of them were abroad. Thankfully, no one has been injured.
In these incidents, the PS Vita has overheated and apparently burned while charging. According to Sony, a manufacturing defect is not to blame and there are no plans for a recall. Sony believes that either liquids or foreign materials entering the charging slot seem to be the cause.
Yomiuri Online reports that the National Institue of Technology and Evaluation, a body from the Japan's Ministry of Economy, Trade and Industry, is investigating the issue.
ＰＳヴィータ焼損３１件、ソニー「欠陥でない」 [Yomiuri Online]