What happened 

Shares of Amkor Technology (AMKR 1.57%) were tumbling today after the company released its first-quarter 2021 results late yesterday. Despite an earnings beat in the quarter, some investors sold off their shares today. 

The tech stock was down by 11.5% as of 3:23 p.m. EDT. 

So what 

Amkor reported sales of $1.33 billion in the first quarter, an increase of 15% year over year, and net income of $120 million. The company's earnings per diluted share in the quarter was $0.49, ahead of analysts' consensus estimate of $0.46 per share. 

A red line pointing down on a dark background.

Image source: Getty Images.

Megan Faust, Amkor's chief financial officer, said in a press release, "Strong operating results and a solid balance sheet provide us the ability to invest in future growth, particularly for Advanced packaging technologies."

When a company beats analysts' consensus earnings estimates, its share price usually climbs. But despite the solid quarter, investors appeared disappointed with the results and pushed Amkor's stock down today. 

Some investors may have been unimpressed with the company's second-quarter outlook. Management estimates that sales will be between $1.29 billion and $1.39 billion and that earnings will be $0.42 per share, at the midpoint of guidance. 

Now what 

Even with today's share price drop, Amkor's stock is still up an impressive 125% over the past 12 months. But since the beginning of this year many tech stocks, including Amkor's, have been pretty volatile. As investors try to gauge how quickly the U.S. economy will recover from the effects of the coronavirus pandemic there could be more instability from Amkor's share price.