Yangtze Memory Technologies Co. is considering an initial public offering in mainland China at a valuation that could exceed $40 billion, according to people familiar with the matter, in what could be one of the biggest listings there in years.YMTC, as the chipmaker is known, may seek a valuation of 200 billion yuan ($28 billion) to 300 billion yuan, and it’s working with China International Capital Corp. and CSC Financial Co. on the potential IPO, the people said, asking not to be identified as...