All investors are happy to see even a modest raise in their stock holdings. On the back of this long bull market we're currently riding, there are a number of companies that have enjoyed quite a big jump. In fact, my research indicates that around 320 stocks have gone up at least 100% in price since the beginning of this year.

That's a daunting number of stocks, yet I've managed to whittle the list down to three names that I think are particularly interesting. Read on to learn more about my chosen trio of doublers.

Two straps of $100 bills, one laid across the other.

Image source: Getty Images.

Universal Display (up 130%)

Organic light-emitting diodes (OLEDs), in spite of their snooze-inducing name, make up one of the hottest technologies in the world right now. These highly efficient semiconductor materials are used to create state-of-the-art TV and smartphone displays and lighting products -- hence their current popularity.

Universal Display (OLED -1.34%) is taking a big ride on this wave. It holds over 4,200 patents in various aspects of OLED technology. It not only sells OLED products to manufacturers of TVs and smartphones, but it also draws licensing revenue from some of those patents and makes money by providing research services to peers.

Business is humming across all of Universal Display's segments. In the company's most recently reported quarter, for example, its materials sales skyrocketed 110% higher on a year-over-year basis to land at nearly $47 million. No wonder total revenue rose by almost 60% to over $102 million.

Slightly more than 50% of the latter figure was due to royalty and license fees the company earned. The beauty of this kind of revenue is that it comes at an extremely low cost. As a result, Universal Display's margins are sky-high -- net margin for the aforementioned quarter was 46%.

OLED is the display technology for now, and the immediate future. And Universal Display has positioned itself to benefit in numerous ways from this trend. No one should be surprised to see this stock glow even brighter.

Corcept Therapeutics (134%)

Corcept Therapeutics (CORT -1.67%)is one of the very few biotechs that actually turns a profit. It netted an adjusted profit of $16 million in its Q2, on revenue that topped $35.5 million. Those two line items, by the way, were up a respective 80% and 407% from the same period last year and trounced analyst expectations.

The leaps in revenue and profit were due to the company's only drug on the market so far -- Korlym, which treats cortisol-related illness Cushing's syndrome. Meanwhile, Corcept has several early to mid-stage products in the pipeline aimed at the treatment of such afflictions as breast cancer and muscular dystrophy.

Although Korlym still has excellent potential as one of the few available Cushing's syndrome drugs, competition looms -- 800-pound pharmaceutical gorilla Novartis also has one treatment on the market, and another more advanced drug in its pipeline. Stonebridge Biopharma's Recorlev, meanwhile, is currently in clinical trials.

Another minus for Corcept Therapeutics is that its pipeline drugs are still in quite early stages of development, and are thus unlikely to approach the market anytime soon.

I also should emphasize that the biotech sector is inherently volatile, and any investment in one of its companies carries a higher-than-average degree of risk. That said, Corcept Therapeutics is doing better than many expected it to and is clearly doing a good job marketing Korlym.

Weight Watchers (271%)

Weight Watchers (WW 14.10%) has become one of 2017's top comeback stories. Since posting unexpectedly strong Q4 2016 results at the beginning of the year, the famous diet-assistance company has since delivered another two blowout quarters. In both, revenue and net profit well exceeded the market's expectations.

Q2 was a fine example of this resurgence. Revenue rose by 10% on a year-over-year basis to almost $342 million, while net income grew by almost 50%. This performance was fueled by a 20%-plus increase in subscriber numbers, which is very impressive considering how long Weight Watchers has been in this game, and how it avoids latching on to trendy diets of the moment.

The good times should continue to roll. So far this year, the company has raised its forward guidance for this fiscal year not once but twice. It now believes it will post per-share net income of $1.57 to $1.67. Before this and the previous guidance increase, it was projecting a tally of only $1.30 to $1.40. By comparison, 2016 EPS was $1.03.

A big reason the stock has leapt so high is that these very positive developments follow a sustained period of disappointment. Oprah Winfrey famously joined Weight Watchers' board in late 2015, but the expected "Oprah effect" on its operations and stock price did not immediately materialize.

Some turnaround stories take longer than expected; Weight Watchers is now living one that feels almost like a fairy tale.