The CEO of Siemens has defended the company's decision to enter the U.S. shale oil space last year, as the group reported a 25 percent drop in net income in the first quarter of 2015.

Speaking to CNBC Europe's "Squawk Box" on Tuesday, Joe Kaeser, president and chief executive officer of Siemens, said the decline in oil prices did not worry him. The German electronics and engineering group acquired American oilfield equipment maker Dresser-Rand in a $7.6 billion deal in September.