Shares of interactive whiteboard maker SMART Technologies are slipping after the company raised $660.1 million in the biggest initial public offering listing in the U.S. this year.

The Canadian company priced 38.8 million Class A shares at $17 apiece late Wednesday. It had expected to offer 35.3 million shares for priced $16 to $18 each.

That makes SMART the biggest deal this year by proceeds. Oil and gas company Oasis Petroleum Inc. raised $588 million in June. But because stockholders sold more than three-quarters of the offering's shares, SMART's proceeds are only about $150 million, before expenses.

Shares, trading Thursday morning on the Nasdaq under the symbol "SMT," are slipping 31 cents to $16.69.