CXMT, one of China’s biggest memory-chip makers, posted sharply higher first-half sales and profit as artificial-intelligence companies competed for scarce memory supplies. The results were the company’s first since its Shanghai listing last month and highlighted the rapid rise of ChangXin Memory Technologies, based in Hefei. CXMT is now the world’s fourth-largest manufacturer of dynamic random access memory, or DRAM (computer memory used for temporary data storage). Its expansion places it at the center of China’s drive for chip self-sufficiency and the broader U.S.-China technology rivalry.