SAN FRANCISCO — Peter Thiel made a relatively modest investment in the presidential candidacy of Donald J. Trump, but it is generating a major uproar in Silicon Valley.

Mr. Trump is toxic among technology investors and entrepreneurs. The news last weekend that Mr. Thiel was giving $1.25 million to the Republican’s campaign is provoking outrage. And tech executives who work with the billionaire investor are being forced to explain why they plan to continue to do business with him.

Now Mr. Thiel will defend himself. A spokesman said Wednesday evening that he would address the controversy in a speech in Washington later this month. He declined to comment further.

Mr. Thiel was the first outside investor in Facebook and sits on its board. That has put the social media giant in the cross hairs of this debate. Mark Zuckerberg, Facebook’s chief executive, warned that cutting ties with Mr. Thiel because of his political views would be a troubling precedent.