美国股市不仅是英伟达、微软等AI龙头昂贵，整体也显得估值偏高：标普500的CAPE（周期调整市盈率）已处于历史上仅在互联网泡沫顶峰出现过的水平。这表明即便存在泡沫担忧，市场对AI革命的乐观预期也已被广泛计入价格。

日本、韩国和台湾同样在今年创下新高，日本半导体测试设备商Advantest自ChatGPT于2022年末发布以来股价已上涨近800%，但估值仍更便宜：三地平均市净率低于3倍，而美国超过5倍，韩国更低至1.4倍。SK海力士今年上涨逾220%，但其预期市盈率约8倍，低于美光的13倍，这也有助于解释其在12月10日宣布正考虑赴美上市以获取更高估值。

该地区更大的风险不是高估值而是集中度：日经指数前五大股票如今占指数价值的36%（2019年为24%），台湾加权指数前五大公司占市值的53%（2019年为30%），使台湾和韩国市场比本已高度集中的美国市场更“头重脚轻”。波动也明显上升：今年日本、韩国和台湾的平均30日已实现波动率比美国高29%，而2020–24年仅高6%，因此即便更低的起点估值缩短下跌距离，AI若崩盘仍会带来重击。

U.S. equities look richly priced beyond AI leaders like Nvidia and Microsoft, with the S&P 500’s CAPE (cyclically adjusted price-earnings) ratio reaching levels previously seen only at the dotcom peak. This suggests broad AI optimism is already embedded in prices despite bubble fears.

Japan, South Korea, and Taiwan have also set records this year, and Japan’s Advantest is up nearly 800% since ChatGPT’s late-2022 release, yet valuations remain cheaper: average price-to-book is under 3× versus over 5× in the U.S., and South Korea sits at 1.4×. SK Hynix has risen over 220% this year but trades around 8× expected earnings versus Micron at 13×, helping explain its December 10 announcement that it is considering a U.S. listing.

The main regional risk is concentration, not overvaluation: the top five Nikkei stocks now represent 36% of index value (24% in 2019), and Taiwan’s top five are 53% of market cap (30% in 2019), making Taiwan and South Korea more top-heavy than the already top-heavy U.S. market. Volatility has also surged, with average 30-day realized volatility running 29% higher than in America this year versus only a 6% gap in 2020–24, so an AI bust would still sting even if lower starting valuations shorten the distance to fall.

Source: Asia’s inexpensive AI stocks should worry American investors

Subtitle: Tech mania looks very different in Japan, South Korea and Taiwan

Dateline: 12月 10, 2025 01:24 下午