The Semiconductor Equipment & Materials International book-to-bill ratio, which gauges demand for chip-equipment tools made in the U.S., rose to 1.3 in March, its sixth straight monthly increase. A ratio of 1.3 means that U.S. makers of semiconductor equipment took in $130 in orders for every $100 of shipments. Anything higher than 1.0 indicates a growing market. SEMI, the Mountain View, Calif., industry group that compiles the book-to-bill, revised the February ratio to 1.21 from 1.17. Orders for new equipment are rising as semiconductor makers ramp up spending after cutting back drastically last year. Average monthly orders, or bookings, for the three months ended in March, rose 14% to $1.15 billion from a revised $1.01 billion in February, according to SEMI.