** Shares of chip designer Ambiq Micro AMBQ.N fall 5.2% to $31.30 premarket

** AMBQ unveils stock offering of 2.2 million shares

** Austin, Texas-based AMBQ is offering 2.16 million shares, while certain stockholders will sell 42,949 shares

** BofA Securities and UBS Investment Bank are joint lead book-running managers for offering

** AMBQ will have 20.4 million outstanding shares after the offering, according to prospectus

** Proceeds will be used for general purposes, including sales and marketing activities, product development and capital expenditure

** Two of four brokerages rate the stock "buy" or higher and two "hold"; median PT $36 - data compiled by LSEG

** As of last close, AMBQ shares up 37.6% since July debut

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com;))