HTC Corp laid off around 20 percent of its U.S.-based staff in what it called a move to streamline its operations after a period of growth, sending its shares tumbling on Monday.

The struggling Taiwanese smartphone maker said it laid off 30 employees on Friday to "optimize our organization and improve efficiencies after several years of aggressive growth".

The company's shares dropped 4 percent by 0122 GMT on Monday, underperforming a 0.9 percent rise in the broader market.

HTC had around 150 employees in the United States - its largest market until last year - before the layoffs, including some design and marketing executives. The company said in a statement that it would "continue to hire in strategic areas".

The U.S. layoffs represent a tiny fraction of HTC's global workforce of about 17,000.

HTC's sales so far this year have dropped 31.5 percent compared to the same period last year, rocked by a component shortage in the beginning of the year and its position at the high end of a smartphone market that is close to saturation.