The Center for Investigative Reporting published a report last month that studied the offshore holdings and tax savings of 50 of the largest publicly traded tech companies in Silicon Valley. The study found that most of the companies in the study keep massive amounts of their cash parked oversees, and that they often use exemptions to avoid reporting the details in their SEC filings.
This chart shows the amounts of cash that eight tech companies have permanently reinvested overseas, rendering those funds permanently safe from U.S. taxation. You can see a full interactive presentation of this data from 50 Silicon Valley companies developed by the Center for Investigative Reporting.