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The return of volatility to the markets after the doldrums of August appears to have pointed short sellers at rival chipmakers Intel and AMD. These two stocks saw the largest upswings in short interest among the most shorted stocks traded on the Nasdaq between the August 31 and September 15 settlement dates. The rest of the top six all saw more modest gains in the number of their shares short.

Note that still only two Nasdaq stocks had more than 100 million shares short by the end of the most recent period. In fact, the top two remain far ahead of the pack.

Sirius XM

The more than 229.41 million Sirius XM Holdings Inc. (NASDAQ: SIRI) shares short by the middle of September was more than 3% higher than on the previous settlement date. That was also the fifth period in a row of short interest above 200 million. Some 13.5% of the company’s float was sold short most recently. At the current average daily volume, it would take more than four days to cover all short positions.

There has been some speculation that weak car sales could be a headwind for Sirius XM. Sirius shares ended the two-week period fractionally higher, largely rising and falling along with the Nasdaq in that time. The stock has retreated somewhat since but is still up more than 2% year to date. It closed most recently at $4.16, in a 52-week trading range of $3.29 to $4.44.

Frontier Communications

The number of shares short in Frontier Communications Corp. (NASDAQ: FTR) has increased in seven of the past eight periods. It rose most recently by over 5% to more than 224.60 million. That was 19.3% of the telecom’s float, as well as the highest short interest in at least a year. The days to cover dropped from about 14 to more than 10 as the average daily volume grew.

Telecoms such as Frontier are cheap compared to the S&P 500. Short sellers watched the shares sink more than 5% in the short interest period, while the Nasdaq was up fractionally. The stock is less than 2% higher in the past week to $4.36. Shares have changed hands between $3.81 and $5.85 in the past year.

MannKind

MannKind Corp.’s (NASDAQ: MNKD) short interest, at more than 99.19 million shares most recently, was more than 3% higher than on the prior settlement date. That was the greatest number of shares short since April, as well as 30.8% of the total float. The daily average volume shrank enough during the period for the days to cover to rise from less than 20 to about 27.

MannKind is one of the companies looking to develop an alternative to the EpiPen. Shares ended the two weeks about 12% lower. They have tumbled more than 16% in the past week and are now more than 60% lower year to date to $0.57, which is a multiyear low. The 52-week high of $3.79 was seen nearly a year ago.

AMD

By the middle of month, Advanced Micro Devices Inc. (NASDAQ: AMD) had almost 80.60 million shares short. That was up nearly 14% from more than 70.78 million on the previous settlement date, which was the lowest short interest so far this year. The latest reading totaled 12.5% of the company’s float. The days to cover ticked down to less than two, which was also a year-to-date low.

While AMD seems to keep defying the skeptical investors, the ending share price was more than 18% lower than on the previous settlement date, though it was down more than 22% at one point in the two weeks. The stock reached a new 52-week high of $8.00 back in August, but shares closed at $6.32 on Monday. The 52-week low is $1.65.

Micron Technology

The number of Micron Technology Inc. (NASDAQ: MU) shares short, at more than 77.13 million by mid-month, was around 4% higher than in the previous period. And it was 7.1% of the total float, as well as the highest level of short interest in the past year. As the daily average volume in the period slipped, the days to cover inched up to more than three.

Analyst sentiment on a Micron recovery increased during the period. The stock rose almost 6%, gave up much of that gain but then ended the two weeks with about a 6% gain. Shares are now up more than 22% since the beginning of the year and closed on Monday at $17.36, in a 52-week range of $9.31 to $19.30.

Intel

More than 75.47 million Intel Corp. (NASDAQ: INTC) shares were sold short as of the most recent settlement date. That was more than 9 million (over 13%) more than at the start of the period, and it totaled 1.6% of the company’s float. It also followed a more than 4% gain in short interest in the previous period. As of mid-September, it would take more than three days to cover all short positions.

Intel was a top Merrill Lynch tech stock pick earlier this month, and the share price ended the two weeks up almost 2% from on the previous settlement date. It is more than 6% higher year to date, and the stock closed at $36.65 on Monday. Shares have changed hands between $27.68 and $38.05 per share in the past 52 weeks.

And Others

Rounding out the top 10 were Opko Health Inc. (NASDAQ: OPK), JD.com Inc. (NASDAQ: JD), Novavax Inc. (NASDAQ: NVAX) and, returning to the top 10, Apple Inc. (NASDAQ: AAPL), with a surge of more than 27 percent in the number of its shares short after the launch of the iPhone 7 and Apple Watch 2.

Lingering just outside the spotlight of the top 10 are the likes of BlackBerry Ltd. (NASDAQ: BBRY), Cisco Systems Inc. (NASDAQ: CSCO), Marriott International Inc. (NASDAQ: MAR) and NVIDIA Corp. (NASDAQ: NVDA).