Should we cheer or fear tech rally?

Technology stocks have accounted for more than half of the gain in the S&P 500 stock index this year. Is the market’s reliance on tech leadership and investors’ love of high flyers such as Amazon a sign of trouble – or a healthy bull?

It has been a tech-centric market this year, with Apple this month becoming the first U.S. publicly traded company to achieve a market value of $1 trillion, and Amazon’s stock on Thursday topping $2,000 for the first time, making it the highest-priced stock in the Standard & Poor’s 500.

Despite all the milestones, and the fact the tech sector (which is up more than 20 percent in 2018) has been a major driver of the broad market gauge’s nearly 9 percent gain this year, the strong business conditions driving tech stocks suggest they’re going up for a reason.

“Tech is being driven by innovation and growth,” says Bill Hornbarger, chief investment officer at Moneta Group in St. Louis. “As long as that story is intact it will continue to be a market leader.”

In the second quarter, tech companies posted profit growth of more than 26 percent, Thomson Reuters data show, with 91 percent of the companies topping forecasts. Hornbarger says today’s tech stocks (which Bespoke Investment Group says are trading at less than 24 times their past 12-month earnings) are not nearly as expensive as they were near the top of the internet stock bubble in 2000, when tech stocks were valued “on clicks and eyeballs.”

Still, loading your portfolio up with too much tech could prove fatal if tech stocks falter.