Updated from 4:15 p.m. to include additional information on Alibaba.

SAN FRANCISCO ( TheStreet) – Twitter (TWTR) - Get Report tanked after reports surfaced that its founder Evan Williams sold shares in the social media company for the first time. Meanwhile, Alibaba (BABA) - Get Report stumbled as U.S. retailers ganged up on the Chinese e-commerce company and On Semiconductor (ONNN) soared after it announced a $1 billion share repurchase program.

Twitter fell 6.5% to close at $39.04 on Monday. The company took a beating after TheWall Street Journal reported late Friday that its founder had sold 719,000 shares that week, ranging in price between $39.83 to $40 a share. The total sale was approximately $28.7 million. 

That sale represented roughly 2% of Williams' Twitter stake. Williams still has plenty of stock, as he held a 9.5% stake in the San Francisco-based company as of March, according to the report.

Twitter went public a year ago, setting its IPO price at $26 a share.

Although investors grew skittish over the sale, one thing to keep in mind it was a pre-arranged trade that was set 90 days ago, according to The Journal. It's a common practice where executives of public companies sell shares under a pre-set plan, in order to reduce the perception that the shares are being sold based on inside knowledge.

Alibaba fell 5.1% to close at $105.99.

The Chinese e-commerce giant is apparently the new target of brick-and-mortar U.S. retailers, who are attempting to turn U.S. lawmakers and consumers against the company, according to a report in the Financial Times. The Alliance for Main Street Fairness, a coalition comprised of retailing titans Target (TGT) - Get Report , Best Buy (BBY) - Get Report , Home Depot (HD) - Get Report , J.C. Penney (JCP) - Get Report and smaller retailers, launched an advertising campaign against Alibaba.

The group alleges Alibaba is taking advantage of a loophole in U.S. tax laws, which enable the e-commerce giant to avoid collecting sales tax on the products it sells. It's a similar allegation that U.S. brick-and-mortar retailers levied against Amazon.com (AMZN) - Get Report , prompting some states to take action and force Amazon and other ecommerce companies to collect sales tax from consumers.

U.S. retailers allege that without collecting sales tax, it gives ecommerce players like Alibaba an unfair advantage by charging consumers less for the product that they purchase on those Web sites.

The coalition's advertising campaign alleges Alibaba's business practices will hurt local retailers unless new laws are passed.

ON Semiconductor soared 5.7% to $9.54 at the close.

Investors gave a thumbs up to the company's plans to issue a $1 billion stock buyback program, as well as a new capital allocation policy. The Arizona-based semiconductor components company said this capital allocation policy would return roughly 80% of its free cash flow back to investors, excluding its long-term debt repayments. 

With regards to the stock repurchase program, it represents a potential repurchase of approximately 111 million shares, or 25%, of the weighted average diluted common shares outstanding as of the end of the company's third quarter, based its closing price on November 28.

On Semiconductor CEO Keith Jackson said in a statement: "We believe that at current levels, our stock offers compelling value, and therefore the repurchase program should deliver substantial value to our shareholders. The long term outlook for our business remains strong, driven by a robust design win pipeline, and we are confident in our ability to generate approximately $300 million to $400 million of annual free cash flow on a sustained basis in the near to mid-term."

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.

TheStreet Ratings team rates ON SEMICONDUCTOR CORP as a Hold with a ratings score of C. TheStreet Ratings Team has this to say about their recommendation:

"We rate ON SEMICONDUCTOR CORP (ONNN) a HOLD. The primary factors that have impacted our rating are mixed ? some indicating strength, some showing weaknesses, with little evidence to justify the expectation of either a positive or negative performance for this stock relative to most other stocks. The company's strengths can be seen in multiple areas, such as its solid stock price performance, revenue growth and reasonable valuation levels. However, as a counter to these strengths, we find that the growth in the company's net income has been quite unimpressive."

You can view the full analysis from the report here: ONNN Ratings Report

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.