KITAKAMI, Japan, July 3 (Reuters) - Kioxia on Friday held a ceremony at its fab in northern Japan as the chipmaker, whose shares have rocketed due to the AI investment boom, begins shipping samples of its next-generation memory. The growth of AI has fueled a remarkable turnaround for Kioxia, which was previously seen as an example of Japan's chipmaking struggles but whose stock price has surged more than sevenfold this year to a market capitalisation over $250 billion, exceeding Toyota Motor's.