Taiwan's top court said Friday it had ordered a new trial for the ex-chief of United Microelectronics Corp, the world's second biggest contract microchip maker, on charges of illegal investments in China. 'The reasons for the (not guilty) verdict are incomplete,' the Supreme Court said in a statement on an earlier trial, adding previous judges failed to take into account witnesses or information against Robert Tsao. Tsao was indicted in 2006 for breach of trust and violation of accounting rules while involved in an investment by UMC in China-based chip maker Hejian Technology. A district court cleared Tsao the following year, saying there was insufficient evidence to prove he provided Hejian with UMC manpower, patents and trade secrets, or helped it raise funds. The High Court upheld the ruling. UMC obtained a 15 percent share in Hejian in a 2005 deal valued at 3.5 billion Taiwan dollars (109 million US dollars), but analysts believe it basically paid in kind via transfer of valuable technologies since early in the decade. The Taiwanese company said it informed the government about the transaction, but the island's authorities insisted the investment broke the law because it was done without prior governmental approval. UMC manufactures cutting-edge microchips that are used in a wide range of electronics, including computers, mobile phones, televisions and cars. The technology is highly prized and safeguarded in Taiwan where many are concerned its longstanding mainland rival could overtake it one day. Tsao stepped down as chairman the day he was indicted in an apparent bid to ease the scandal's impact on UMC. The company had described the indictment as of 'purely political nature' caused by tensions at the time between Taiwan and China. Ties hit rock-bottom during the 2000-2008 term of former Taiwanese president Chen Shui-bian, who often irked Beijing with his policies pushing for the island's independence. 