The Globe and Mail reports in its Wednesday, June 21, edition that S&P 500 has entered bull-market territory owing to highly profitable tech companies. The Globe's guest columnist George Athanassakos writes that if you exclude the seven largest tech stocks, the S&P 500 has been mostly flat. Many wonder whether we have we seen this movie before and whether another bubble is being formed, one that will target the most profitable U.S. tech stocks. Large-cap U.S. tech stocks are currently trading at extreme valuations. Nvidia trades at a price-to-earnings ratio of 205 times, Apple 30 times, Tesla 62 times and Alphabet 28 times earnings. The S&P 500 PE is 24 times, the U.S. tech sector PE is 42 times and the semiconductor 51 times. Large-cap tech stocks are expensive relative to markets in general and to historical averages. Tech companies are booming based on optimism and related artificial-intelligence euphoria that global productivity will soar with the new technologies and the belief that inflation and interest rates are heading down. If inflation and interest rates continue to rally, and euphoria on AI dissipates, Mr. Athanassakos believes we may then see a stock market bubble like no other.