Picking the next billion dollar tech company whilst it is still a small cap share is a great way of making incredible returns. Just ask investors who bought TPG Telecom Ltd (ASX: TPM) shares back in March of 2009.

Just under seven-an- a-half years ago you could buy TPG Telecom shares for 13 cents apiece, whereas today they are currently changing hands at $12.68. This means that a $10,000 investment at that point would be worth a massive $975,000 today from share price gains alone. Factor in the dividends and you are well and truly beyond $1 million dollars.

Whilst picking the next TPG Telecom is near impossible, I believe these four tech shares certainly have the potential to become billion dollar companies in the future.

Afterpay Holdings Ltd (ASX: AFY)

This growing fintech company provides online retailers with the option to allow their customers to buy goods now, but pay for them later without interest or fees. Afterpay takes a small percentage of the sale in exchange for bearing its default risk. It has been growing its client list at an impressive clip and includes retailers such as General Pants Co and CUE. The latter has recently been trialling its services in its bricks-and-mortar stores, with management advising that results have been very encouraging thus far.

Appen Ltd (ASX: APX)

This language technology data and services company is definitely one to watch in my opinion. Being the market leader in an industry exhibiting strong growth, I believe Appen has enormous growth potential that would make it a great long-term investment today. Its services are being used by government security agencies and some of the world’s leading technology companies such as Microsoft and Facebook.

iSentia Group Ltd (ASX: ISD)

The global leader in the delivery of crucial business intelligence produced half year underlying net profit after tax and amortisation growth of 22%. This is partly thanks to the growing popularity of its Mediaportal platform. The platform provides a cloud-based workspace which delivers news as and when it happens, together with analytics and reporting tools. There are concerns that its strong first half growth in the Asia market was mainly attributable to favourable currency movements. I’ll be looking for signs of strong organic growth in its full year results.

Touchcorp Ltd (ASX: TCH)

Touchcorp is a provider of secure transaction processing technology and counts companies such as 7-Eleven, Afterpay, Optus, and HICAPS amongst its growing client list. Recent deals with Switzerland’s Cornèr Bank and Change Up Holdings for activities in Sweden and Norway go to show that this is a company with global ambitions. Both of the deals are expected to provide the company with long-term transactional revenue streams. The company not only provides its services for Afterpay, but also owns around 30% of it. An investment in Touchcorp is therefore a great way of getting exposure to both of these exciting fintech companies.

Lastly, before you add any of these four tech shares to your portfolio I would highly recommend you check to see if you own any of these three rotten ASX shares. Now could be a great time to swap them out before they damage your portfolio.

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia owns shares of TOUCHCORP FPO. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.