The tech sector is fertile ground for growth and innovation, and this can be enormously profitable for investors over the long term. Furthermore, industry giants such as Apple (NASDAQ:AAPL), Google (NASDAQ:GOOG) (NASDAQ:GOOGL), and (NASDAQ:AMZN) have consolidated rock-solid competitive positions in their respective businesses. Thus, they look well positioned to continue delivering big gains for investors in 2015 and beyond.

With a market capitalization of roughly $740 billion, Apple has become the biggest listed corporation on the planet. Growth naturally tends to slow down as a company gains size, because it's much easier to deliver rapid growth from a small revenue base. However, Apple continues producing spectacular financial performance in spite of its massive scale, proving that the company is truly one of a kind.

Apple delivered a 27% year-over-year increase in sales last quarter, reaching a gargantuan $58 billion during the period. Profit margins are on the rise due to sales leverage and strong pricing for the company's iPhone 6 and iPhone 6 Plus models.

In addition, the company is allocating massive amounts of money to stock repurchases, reducing the amount of shares outstanding and boosting earnings per share. This is allowing Apple to deliver earnings growth well above revenue increases -- in the neighborhood of 40% year over year in the last quarter.

Source: Apple.

The iPhone generates most of Apple's sales and earnings. While this is a powerful driver on the back of booming demand for the latest models, it also represents a considerable source of risk due to product concentration. However, Apple is actively betting on innovation in order to diversify its revenue stream and open additional growth venues.

Apple Pay is off to a promising start, and success in this business would allow Apple to generate recurring revenue from its massive installed base as opposed to selling new devices. While it's far too early to tell how Apple Watch will do, Apple's brand power and extraordinary design capabilities bode well for the company as it enters the smartwatch industry.

According to CEO Tim Cook, there are already more than 3,500 apps available for Apple Watch, so developers are clearly jumping on board. This is quite encouraging in terms of evaluating Apple Watch's chances of success.

When a company's name becomes a synonym for the product or service that the business is offering, you know you're talking about an exceptionally strong brand. Google is so ingrained in consumers' minds that people "google" for information as opposed to searching for it online. According to data from StatCounter, Google owns a gargantuan market share of more than 90% when considering both desktop and mobile search on a global basis.

Most of the growth in online traffic is coming from mobile, an area where Google is remarkably well positioned. Its Android operating system is massively popular, with more than 1 billion users around the world.

Furthermore, Google owns enormously valuable services and applications such as Chrome, YouTube, and Google Maps, among several others. These applications are among the most popular in both Android and IOS, so Google is in all the right places to capitalize on the mobile revolution.

As advertising money continues shifting from traditional media to online, Google will most likely capture a big share of that industry growth. Google uses the information it collects from its users to provide better search results and more effective advertising. The bigger Google gets, the smarter and more effective it becomes over time.

The key financial variables are also moving in the right direction. Constant-currency revenue increased by 17% year over year in the first quarter of 2015, and Google generates big profit margins in the area of 26% of revenue.

Amazon is all about building competitive strength and capitalizing on its long-term opportunities, even at the expense of its profit margin. The company sells its products for razor-thin profit margins on order to gain market share. It's also investing tons of money in areas such as building its distribution network, digital content, and its AWS cloud-computing division.

This means that, unlike Apple or Google, Amazon does not make a lot of money on sales. In fact, the company's net income was negative last quarter. Amazon is probably not the best choice for investors looking for businesses with big and predictable earnings. On the other hand, the company is second to none when it comes to growth and innovative potential.

Amazon has been arguably the most disruptive force in the retail industry during the last decade. As the company gains scale and it consolidates its logistics capabilities, its competitive position is only getting stronger over time.

According to the latest financial report, there's no slowdown in sight for the online retail giant. Amazon delivered a big increase of 22% in constant-currency sales during the first quarter of 2015. This represents acceleration versus an 18% increase in constant-currency sales in the fourth quarter of 2014.

Also, the last quarter was the first time that Amazon disclosed financial information for its AWS segment, and the business looks remarkably strong. Sales during the quarter were $1.57 billion, growing by an impressive 49% year over year. AWS is also quite profitable: Segment operating income was $265 million during the period.

Amazon's profit margin will remain hard to predict for now; however, Amazon offers enormous opportunities for long-term growth as the undisputed leader in both online retail and cloud-computing infrastructure.