A lot of times, market cap isn't the best measure. The difference in market cap between MSFT and AAPL is similar to their difference in P/E (AAPL has a higher P/E than MSFT and INTC). Also, MSFT pays out a 2.70% dividend. With AAPL, you get nothing. What this really shows is that investors on the whole are optimistic that AAPL will outperform MSFT going forward. This can change on a dime, but right now AAPL is more popular in the eyes of investors. That makes their shares more expensive. However, it's really just a guessing game.