Amazon has announced a record profit for the last three months of close to $3bn. But the news on Thursday of a $1bn-a-month bonanza was not enough for Wall Street and shares sank on lower-than-expected revenue growth.

The online retail and cloud computing giant long worried investors by losing cash quarter after quarter but now appears to be raking in money, thanks largely to its cloud computing services. In the last quarter the company made a profit of $2.88bn, the fourth quarter that Amazon’s profits have been greater than $1bn.

Sales grew close to 30% to $56.58bn in the third quarter but were lower than the $57.1bn analysts had estimated. Shares sank close to 6% in after hours trading but were up close to 49% this year before the latest news.

Once again Amazon Web Services, the company’s fast-growing cloud services business, was the star performer for the company. Revenues surged 45.7% to $6.68bn.

The company’s costs are rising. Amazon recently announced it would raise the minimum wage at its warehouses to $15 an hour, a move that was applauded by the former, and possibly future, Democratic presidential hopeful Bernie Sanders. The wage rise is expected to cost $3bn next year. Amazon is also spending heavily on media as it competes with Netflix and gears up for the holiday season.

In a statement, Amazon’s chief executive, Jeff Bezos, highlighted the growth of Amazon Business, its marketplace for business customers. “Amazon Business has now reached a $10bn annual sales run rate and is serving millions of private and public-sector organizations in eight countries,” Bezos said.