. SoftBank Corp's logo is pictured at a news conference in Tokyo, Japan, February 4, 2021. /Kim Kyung-HoonBy Sam Nussey TOKYO SoftBank Group Corp shares tumbled 8% in morning trade on Thursday after the conglomerate did not extend its buyback programme, removing support for the stock as concern over frothy portfolio valuations outweighed record earnings. SoftBank completed a 2.5 trillion yen ($22.8 billion) buyback on Wednesday, though Chief Executive Masayoshi Son said further repurchases remain an option. SoftBank reported record profit following the listing of e-commerce firm Coupang Inc, but shares of investments including Coupang and Doordash Inc have since been caught in a tech sell-off while top asset Alibaba (NYSE:BABA) Group Holding Ltd has been hit by a regulatory crackdown. "Without the buyback, SoftBank's stock price is likely to reflect the performance of its listed investments," Jefferies (NYSE:JEF) analyst Atul Goyal wrote in a client note, adding he was "extremely surprised" SoftBank did not extend the programme. The slide in SoftBank shares extends this week's decline to 17%, with market observers continuing to express concern that valuations are too high amid rock bottom interest rates. The largest asset in the Vision Fund's portfolio, Coupang, is expensive compared to peers and "despite the intense sell-off there is no valuation driven bottom in sight," LightStream Research analyst Mio Kato wrote on the Smartkarma platform. Doordash and Uber Technologies (NYSE:UBER) are "also unsustainably valued," Kato added, pointing to their money losing business models and Uber's worsening debt position. SoftBank executives point to a robust pipeline of startups preparing to list. Vision Fund 2, which is cutting smaller cheques than the first fund, has completed or approved investments in almost 100 startups.