Amazon.com shares hit all-time highs Friday above the psychologically key $800 level, making the online merchant one of the five largest U.S. companies by market capitalization.
The growth of Amazon's stock is emblematic of a gradual rise among tech or technology-related stocks that are in the . Such companies now dominate the top of the index.
"The reason why these stocks are there (is) in an economy that's hardly growing, growth stocks demand a high premium," said Bruce Bittles, chief investment strategist at Baird.
Technology stocks are considered growth stocks, which move sharply on momentum, versus so-called value stocks that are less volatile and generally represent industries more connected to economic fundamentals such as oil prices.