A ratio that shows the relationship between semiconductor orders and billings. A book-to-bill of 1.28 means that $128 worth of new orders were received for every $100 of product billed for the month. A San Jose, California-based trade association, the Semiconductor Equipment and Materials International (SEMI), reports book-to-bill data monthly for North America using three-month moving averages. Companies in the semiconductor industry often release their own book-to-bill ratios. The statistic is widely watched in the technology market to judge how well semiconductor companies are performing.