** Shares of chip designer Cerebras Systems CBRS.O up 2% at $317.50 premarket a day after Nasdaq debut

** Stock opens at $350 vs IPO price of $185, valuing chip designer at roughly $106.75 bln on a fully diluted basis

** Sunnyvale, California-based co raises $5.55 bln in its U.S. IPO, the largest listing so far this year

** CBRS designs wafer-scale chips aimed at accelerating AI workloads, packing hundreds of thousands of compute cores onto a single processor

** Sources told Reuters that the offering had drawn orders for more than 20 times the number of shares available

** CBRS has secured Amazon AMZN.O and OpenAI, two of the biggest builders of AI infrastructure in the world, as customers