North American makers of equipment to produce semiconductors saw orders fall 17 percent from a year ago to $1.44 billion in July, a U.S. trade group said on Thursday.

The book-to-bill ratio, which compares the volume of orders to products shipped, was 0.84 in the period, Semiconductor Equipment and Materials International said. That means $84 of orders were received for every $100 of product billed.

Orders have slowed from the strong levels observed in the first part of this year and are at levels last seen in November of 2006, SEMI President and Chief Executive Stanley Myers said in a statement.

The group reported that $1.7 billion worth of equipment had been billed in July, according to preliminary figures.

Final figures for June showed a book-to-bill of 0.91, based on $1.61 billion in bookings and $1.77 billion in billing. (Reporting by Peter Henderson)